feat(desktop): align sidebar app rail

.qwen/e2e-tests/electron-desktop/sidebar-app-rail-fidelity.md

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+# Sidebar App Rail Prototype Fidelity
+
+- Slice date: 2026-04-26
+- Executable harness: `packages/desktop/scripts/e2e-cdp-smoke.mjs`
+- Command:
+  `cd packages/desktop && npm run e2e:cdp`
+- Result: pass
+- Passing artifact directory:
+  `.qwen/e2e-tests/electron-desktop/artifacts/2026-04-26T01-46-17-523Z/`
+
+## Scenario
+
+1. Launch the real Electron app with isolated HOME, runtime, user-data, and a
+   fake dirty Git workspace.
+2. Open the fake project through the desktop directory picker path.
+3. Send the first composer prompt and approve the fake command request.
+4. Wait for the fake ACP response and changed-files summary.
+5. Assert the left sidebar uses compact top app actions, project/thread browser
+   sections, and a persistent bottom Settings row.
+6. Continue the existing assistant actions, changed-files summary, review
+   drawer, compact layout, settings, terminal, discard safety, and commit smoke
+   path.
+
+## Assertions
+
+- `data-testid="sidebar-app-actions"` and
+  `data-testid="sidebar-footer-settings"` are present in the real Electron DOM.
+- Top app action labels are `New Thread`, `Open Project`, and `Models`.
+- The old `.sidebar-toolbar` is absent.
+- Bottom Settings is below the project/thread browser and contained in the
+  sidebar.
+- Sidebar width stays compact at `272` px in the default viewport.
+- App action rows are `32` px high, the project row is `39.75` px high, and the
+  thread row is `36` px high.
+- Sidebar rows and regions have no horizontal overflow.
+- Sidebar text does not expose fake ACP session IDs, `Connected to ...`
+  protocol text, or temp full paths.
+- Console errors: 0.
+- Failed local network requests: 0.
+
+## Artifacts
+
+- `sidebar-app-rail.json`
+- `initial-workspace.png`
+- `completed-workspace.png`
+- `electron.log`
+- `summary.json`
+
+## Known Uncovered Risk
+
+The harness covers one project, one thread, and bounded labels. A dedicated
+long-label CDP path is still needed for very long project names, branch names,
+model names, and review-open compact widths.