feat(cli): TUI component architecture — status bars, message list, input bar

- Split monolithic app.tsx into composable components:
  - TopBar: connection indicator (●/○), gateway URL, model name, conversation ID
  - BottomBar: cwd, git branch, token usage
  - MessageList: timestamped messages, tool call indicators, thinking display
  - InputBar: context-aware prompt with streaming/disconnect states
- Extract socket logic into useSocket hook with typed events
- Extract git/cwd info into useGitInfo hook
- Quiet disconnect: single indicator instead of error flood
- Add @mosaic/types dependency for typed Socket.IO events
- Add PRD and task tracking docs

Tasks: TUI-001 through TUI-007 (Wave 1)

packages/cli/src/tui/hooks/use-git-info.ts

@@ -0,0 +1,29 @@
+import { useState, useEffect } from 'react';
+import { execSync } from 'node:child_process';
+
+export interface GitInfo {
+  branch: string | null;
+  cwd: string;
+}
+
+export function useGitInfo(): GitInfo {
+  const [info, setInfo] = useState<GitInfo>({
+    branch: null,
+    cwd: process.cwd(),
+  });
+
+  useEffect(() => {
+    try {
+      const branch = execSync('git rev-parse --abbrev-ref HEAD', {
+        encoding: 'utf-8',
+        timeout: 3000,
+        stdio: ['pipe', 'pipe', 'pipe'],
+      }).trim();
+      setInfo({ branch, cwd: process.cwd() });
+    } catch {
+      setInfo({ branch: null, cwd: process.cwd() });
+    }
+  }, []);
+
+  return info;
+}