feat(ui): rewrite customizable status line

Rewrite the status line feature (originally by Gemini 3.1 Pro) to align
with the upstream design:

- Settings: change from plain string to object `{ type, command, padding? }`
- Hook: event-driven with 300ms debounce instead of 5s polling; pass
  structured JSON context (session, model, tokens, vim) via stdin;
  generation counter to ignore stale exec callbacks; EPIPE guard on stdin
- Footer: render status line as dedicated row with dimColor + truncate;
  suppress "? for shortcuts" hint when status line is active
- Add `/statusline` slash command that delegates to a statusline-setup agent
- Add `statusline-setup` built-in agent with PS1 conversion instructions
- Remove unrelated changes (whitespace, formatting, package-lock, test file)
- Fix copyright headers (Google LLC → Qwen)
- Fix config path references (~/.qwen-code → ~/.qwen)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/cli/src/ui/commands/statuslineCommand.ts

@@ -0,0 +1,29 @@
+/**
+ * @license
+ * Copyright 2025 Qwen
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type { SlashCommand, SubmitPromptActionReturn } from './types.js';
+import { CommandKind } from './types.js';
+import { t } from '../../i18n/index.js';
+
+export const statuslineCommand: SlashCommand = {
+  name: 'statusline',
+  get description() {
+    return t("Set up Qwen Code's status line UI");
+  },
+  kind: CommandKind.BUILT_IN,
+  action: (_context, args): SubmitPromptActionReturn => {
+    const prompt =
+      args.trim() || 'Configure my statusLine from my shell PS1 configuration';
+    return {
+      type: 'submit_prompt',
+      content: [
+        {
+          text: `Create an Agent with subagent_type "statusline-setup" and the following prompt:\n\n${prompt}`,
+        },
+      ],
+    };
+  },
+};