feat(extensions): add GNOME Shell extension for native panel feel

Ship a GJS extension in extensions/gnome-shell/codeburn@agentseal.org so
GNOME users get the same panel-anchored popover Ubuntu's Quick Settings
uses, rather than the floating window the Tauri tray is limited to through
StatusNotifierItem.

The extension lives inside gnome-shell as a PanelMenu.Button, so it has
direct access to its own icon coordinates and can open a PopupMenu docked
under it without any IPC or DBus plumbing. The tradeoff is it only works
on GNOME 45+; the Tauri app in desktop/ stays the cross-platform option
for KDE, Unity, wlroots, and Windows users.

Data flow: the extension shells out to codeburn status --format menubar-json
every 60 seconds, parses the payload, and renders a header, top 5 activities,
and optimize findings count. Refresh and Open Full Report actions live in
the popup menu; the Open Full Report action spawns gnome-terminal with the
codeburn report TUI.

extensions/gnome-shell/README.md

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+# CodeBurn GNOME Shell extension
+
+Native GNOME panel button that shows today's AI coding spend with a click-to-open popover, matching the feel of Ubuntu's Quick Settings menu.
+
+This is an alternative to the cross-platform Tauri tray app in `../desktop/`. Use this on GNOME for the most native UX. The Tauri app stays the right choice for KDE, Unity, wlroots compositors, Windows, and headless systems.
+
+## Requirements
+
+* GNOME Shell 45, 46, 47, or 48 (Ubuntu 22.04 LTS, 24.04 LTS, and Fedora 39+)
+* `codeburn` CLI on PATH (`npm install -g codeburn`)
+
+## Install (from source, local user)
+
+```bash
+cp -r extensions/gnome-shell/codeburn@agentseal.org ~/.local/share/gnome-shell/extensions/
+gnome-extensions enable codeburn@agentseal.org
+```
+
+Then restart GNOME Shell so the extension loads:
+
+* **X11:** press `Alt + F2`, type `r`, press Enter.
+* **Wayland:** log out and log back in (GNOME on Wayland has no in-session shell restart).
+
+## What it shows
+
+Panel button:
+* 🔥 icon
+* Today's cost (e.g. `$24.73`)
+
+Popup menu:
+* Header: period + cost + call count + session count
+* Top 5 activities (Coding, Debugging, Testing, etc.) with per-activity cost and turn count
+* Optimize findings count with potential savings (if any)
+* Refresh and Open Full Report actions
+
+Data refreshes every 60 seconds. Right-click the panel button to open the default panel context menu.
+
+## Uninstall
+
+```bash
+gnome-extensions disable codeburn@agentseal.org
+rm -rf ~/.local/share/gnome-shell/extensions/codeburn@agentseal.org
+```
+
+## Development
+
+Run a nested shell to iterate without restarting your session (X11 only):
+
+```bash
+dbus-run-session -- gnome-shell --nested --wayland
+```
+
+Tail the extension log:
+
+```bash
+journalctl -f -o cat /usr/bin/gnome-shell
+```
+
+The extension uses the GNOME 45+ ESM-based extension API (`import` + `Extension` class). It will not load on GNOME 44 or earlier.

extensions/gnome-shell/codeburn@agentseal.org/extension.js

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+/*
+ * CodeBurn GNOME Shell extension.
+ *
+ * Renders a flame + today's cost label in the top panel and opens a native
+ * PopupMenu on click, matching Ubuntu's Quick Settings feel. Unlike the Tauri
+ * tray app (desktop/), this lives inside gnome-shell so it can anchor the
+ * popover directly under its panel button without going through SNI.
+ *
+ * Data source: `codeburn status --format menubar-json`, polled every 60s.
+ */
+
+import GObject from 'gi://GObject';
+import St from 'gi://St';
+import Gio from 'gi://Gio';
+import GLib from 'gi://GLib';
+import Clutter from 'gi://Clutter';
+
+import * as Main from 'resource:///org/gnome/shell/ui/main.js';
+import * as PanelMenu from 'resource:///org/gnome/shell/ui/panelMenu.js';
+import * as PopupMenu from 'resource:///org/gnome/shell/ui/popupMenu.js';
+import {Extension} from 'resource:///org/gnome/shell/extensions/extension.js';
+
+const REFRESH_INTERVAL_SECONDS = 60;
+const TOP_ACTIVITIES = 5;
+const CODEBURN_BIN = 'codeburn';
+
+const CodeburnIndicator = GObject.registerClass(
+class CodeburnIndicator extends PanelMenu.Button {
+    _init() {
+        super._init(0.0, 'CodeBurn');
+
+        const box = new St.BoxLayout({style_class: 'panel-status-menu-box codeburn-panel'});
+        this._flame = new St.Label({
+            text: '🔥',
+            y_align: Clutter.ActorAlign.CENTER,
+            style_class: 'codeburn-flame',
+        });
+        this._label = new St.Label({
+            text: '…',
+            y_align: Clutter.ActorAlign.CENTER,
+            style_class: 'codeburn-label',
+        });
+        box.add_child(this._flame);
+        box.add_child(this._label);
+        this.add_child(box);
+
+        this._headerItem = new PopupMenu.PopupMenuItem('Loading…', {reactive: false});
+        this._headerItem.label.style_class = 'codeburn-header';
+        this.menu.addMenuItem(this._headerItem);
+        this.menu.addMenuItem(new PopupMenu.PopupSeparatorMenuItem());
+
+        this._activitySection = new PopupMenu.PopupMenuSection();
+        this.menu.addMenuItem(this._activitySection);
+
+        this._findingsSection = new PopupMenu.PopupMenuSection();
+        this.menu.addMenuItem(this._findingsSection);
+
+        this.menu.addMenuItem(new PopupMenu.PopupSeparatorMenuItem());
+
+        const refresh = new PopupMenu.PopupMenuItem('Refresh');
+        refresh.connect('activate', () => this._refresh());
+        this.menu.addMenuItem(refresh);
+
+        const openReport = new PopupMenu.PopupMenuItem('Open Full Report');
+        openReport.connect('activate', () => this._spawnTerminal([CODEBURN_BIN, 'report']));
+        this.menu.addMenuItem(openReport);
+
+        this._refresh();
+        this._timeout = GLib.timeout_add_seconds(
+            GLib.PRIORITY_DEFAULT,
+            REFRESH_INTERVAL_SECONDS,
+            () => {
+                this._refresh();
+                return GLib.SOURCE_CONTINUE;
+            },
+        );
+    }
+
+    _refresh() {
+        let proc;
+        try {
+            proc = Gio.Subprocess.new(
+                [CODEBURN_BIN, 'status', '--format', 'menubar-json'],
+                Gio.SubprocessFlags.STDOUT_PIPE | Gio.SubprocessFlags.STDERR_PIPE,
+            );
+        } catch (e) {
+            this._renderError(`codeburn CLI not found on PATH. Install the npm package first.`);
+            return;
+        }
+
+        proc.communicate_utf8_async(null, null, (p, result) => {
+            try {
+                const [ok, stdout, stderr] = p.communicate_utf8_finish(result);
+                if (!ok) {
+                    this._renderError(`codeburn failed: ${stderr || 'unknown error'}`);
+                    return;
+                }
+                if (!stdout) {
+                    this._renderError('codeburn returned no output');
+                    return;
+                }
+                const payload = JSON.parse(stdout);
+                this._render(payload);
+            } catch (e) {
+                this._renderError(`parse error: ${e.message}`);
+            }
+        });
+    }
+
+    _render(payload) {
+        const current = payload?.current ?? {};
+        const cost = Number(current.cost ?? 0);
+        const formatted = formatUsd(cost);
+        this._label.set_text(formatted);
+
+        const label = current.label ?? '';
+        const calls = current.calls ?? 0;
+        const sessions = current.sessions ?? 0;
+        this._headerItem.label.set_text(
+            `${label}  ${formatted}  ${calls.toLocaleString()} calls  ${sessions} sessions`,
+        );
+
+        this._activitySection.removeAll();
+        const activities = Array.isArray(current.topActivities) ? current.topActivities : [];
+        if (activities.length === 0) {
+            const empty = new PopupMenu.PopupMenuItem('No activity for this period', {reactive: false});
+            empty.label.style_class = 'codeburn-empty';
+            this._activitySection.addMenuItem(empty);
+        } else {
+            for (const a of activities.slice(0, TOP_ACTIVITIES)) {
+                const line = `${a.name}   ${formatUsd(a.cost)}   ${a.turns} turns`;
+                const item = new PopupMenu.PopupMenuItem(line, {reactive: false});
+                item.label.style_class = 'codeburn-activity';
+                this._activitySection.addMenuItem(item);
+            }
+        }
+
+        this._findingsSection.removeAll();
+        const findingCount = payload?.optimize?.findingCount ?? 0;
+        if (findingCount > 0) {
+            this._findingsSection.addMenuItem(new PopupMenu.PopupSeparatorMenuItem());
+            const savings = Number(payload.optimize.savingsUSD ?? 0);
+            const text = `${findingCount} optimize findings   save ~${formatUsd(savings)}`;
+            const item = new PopupMenu.PopupMenuItem(text);
+            item.label.style_class = 'codeburn-findings';
+            item.connect('activate', () => this._spawnTerminal([CODEBURN_BIN, 'optimize']));
+            this._findingsSection.addMenuItem(item);
+        }
+    }
+
+    _renderError(message) {
+        this._label.set_text('!');
+        this._headerItem.label.set_text(message);
+        this._activitySection.removeAll();
+        this._findingsSection.removeAll();
+    }
+
+    _spawnTerminal(argv) {
+        // Quote arguments into a single command string for bash -lc. argv here only ever
+        // contains static identifiers from our own code so plain join is safe.
+        const command = `${argv.join(' ')}; echo; read -n 1 -s -r -p 'Press any key to close...'`;
+        try {
+            Gio.Subprocess.new(
+                ['gnome-terminal', '--', 'bash', '-lc', command],
+                Gio.SubprocessFlags.NONE,
+            );
+        } catch (e) {
+            log(`codeburn: terminal spawn error: ${e.message}`);
+        }
+    }
+
+    destroy() {
+        if (this._timeout) {
+            GLib.source_remove(this._timeout);
+            this._timeout = null;
+        }
+        super.destroy();
+    }
+});
+
+function formatUsd(value) {
+    const abs = Math.abs(value);
+    if (abs >= 1000) {
+        return `$${(value / 1000).toFixed(abs >= 10000 ? 0 : 1)}k`;
+    }
+    return `$${value.toFixed(2)}`;
+}
+
+export default class CodeburnExtension extends Extension {
+    enable() {
+        this._indicator = new CodeburnIndicator();
+        Main.panel.addToStatusArea('codeburn', this._indicator);
+    }
+
+    disable() {
+        this._indicator?.destroy();
+        this._indicator = null;
+    }
+}

extensions/gnome-shell/codeburn@agentseal.org/metadata.json

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+{
+  "uuid": "codeburn@agentseal.org",
+  "name": "CodeBurn",
+  "description": "Ambient AI coding cost tracker for Claude Code, Codex, Cursor, and Copilot. Shows today's spend in the top panel with a dashboard popover.",
+  "shell-version": ["45", "46", "47", "48"],
+  "url": "https://github.com/AgentSeal/codeburn",
+  "session-modes": ["user"]
+}

extensions/gnome-shell/codeburn@agentseal.org/stylesheet.css

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+.codeburn-panel {
+    spacing: 4px;
+}
+
+.codeburn-flame {
+    font-size: 14px;
+}
+
+.codeburn-label {
+    font-weight: 500;
+    padding-left: 2px;
+    padding-right: 2px;
+}
+
+.codeburn-header {
+    font-weight: 600;
+    color: #ff8c42;
+}
+
+.codeburn-activity {
+    font-family: monospace;
+    font-size: 11px;
+    padding-left: 8px;
+}
+
+.codeburn-empty {
+    font-style: italic;
+    color: rgba(255, 255, 255, 0.5);
+    padding-left: 8px;
+}
+
+.codeburn-findings {
+    color: #ff8c42;
+    font-weight: 500;
+}