feat: workspace git detection with branch/status badge

When the workspace root is a git repo, a badge in the panel header
shows the current branch name, dirty file count, and ahead/behind
status. Updates on every root directory load.

Backend:
- git_info_for_workspace() in api/workspace.py runs lightweight git
  commands (rev-parse, status --porcelain, rev-list) with 3s timeout
- New GET /api/git-info endpoint returns branch, dirty count, modified,
  untracked, ahead, behind

Frontend:
- _refreshGitBadge() in workspace.js fetches git info on root load
- Git badge element in panel header shows branch + status
- Badge turns gold when workspace has uncommitted changes

Inspired by PR #75 (@MartinNielsenDev).

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

api/routes.py

@@ -214,6 +214,18 @@ def handle_get(handler, parsed):
     if parsed.path == '/api/list':
         return _handle_list_dir(handler, parsed)
 
+    if parsed.path == '/api/git-info':
+        qs = parse_qs(parsed.query)
+        sid = qs.get('session_id', [''])[0]
+        if not sid:
+            return bad(handler, 'session_id required')
+        s = get_session(sid)
+        if not s:
+            return bad(handler, 'Session not found', 404)
+        from api.workspace import git_info_for_workspace
+        info = git_info_for_workspace(Path(s.workspace))
+        return j(handler, {'git': info})
+
     if parsed.path == '/api/chat/stream/status':
         stream_id = parse_qs(parsed.query).get('stream_id', [''])[0]
         return j(handler, {'active': stream_id in STREAMS, 'stream_id': stream_id})

api/workspace.py

@@ -9,6 +9,7 @@ paths are used as fallback when no profile module is available.
 """
 import json
 import os
+import subprocess
 from pathlib import Path
 
 from api.config import (
@@ -243,3 +244,43 @@ def read_file_content(workspace: Path, rel: str):
         raise ValueError(f"File too large ({size} bytes, max {MAX_FILE_BYTES})")
     content = target.read_text(encoding='utf-8', errors='replace')
     return {'path': rel, 'content': content, 'size': size, 'lines': content.count('\n') + 1}
+
+
+# ── Git detection ──────────────────────────────────────────────────────────
+
+def _run_git(args, cwd, timeout=3):
+    """Run a git command and return stdout, or None on failure."""
+    try:
+        r = subprocess.run(
+            ['git'] + args, cwd=str(cwd), capture_output=True,
+            text=True, timeout=timeout,
+        )
+        return r.stdout.strip() if r.returncode == 0 else None
+    except (subprocess.TimeoutExpired, FileNotFoundError, OSError):
+        return None
+
+
+def git_info_for_workspace(workspace: Path) -> dict:
+    """Return git info for a workspace directory, or None if not a git repo."""
+    if not (workspace / '.git').exists():
+        return None
+    branch = _run_git(['rev-parse', '--abbrev-ref', 'HEAD'], workspace)
+    if branch is None:
+        return None
+    # Status counts
+    status_out = _run_git(['status', '--porcelain'], workspace) or ''
+    modified = sum(1 for l in status_out.splitlines() if l and l[0:2].strip() in ('M', 'MM', 'AM'))
+    untracked = sum(1 for l in status_out.splitlines() if l.startswith('??'))
+    dirty = len(status_out.splitlines()) if status_out else 0
+    # Ahead/behind
+    ahead = _run_git(['rev-list', '--count', '@{u}..HEAD'], workspace)
+    behind = _run_git(['rev-list', '--count', 'HEAD..@{u}'], workspace)
+    return {
+        'branch': branch,
+        'dirty': dirty,
+        'modified': modified,
+        'untracked': untracked,
+        'ahead': int(ahead) if ahead and ahead.isdigit() else 0,
+        'behind': int(behind) if behind and behind.isdigit() else 0,
+        'is_git': True,
+    }