fix(doctor): detect missing git repo and improve daemon startup message (#890)

When not in a git repository:
- Daemon startup now shows clear message immediately instead of waiting
  5 seconds: "Note: No git repository initialized — running without
  background sync"
- Added new doctor check "Git Sync Setup" that explains the situation

Doctor check now shows three states:
1. No git repo → Warning with fix: "Run 'git init' to enable background sync"
2. Git repo, no sync-branch → OK with hint about team collaboration benefits
3. Git repo + sync-branch → OK, fully configured

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/daemon_autostart.go

@@ -310,6 +310,14 @@ func determineSocketPath(socketPath string) string {
 }
 
 func startDaemonProcess(socketPath string) bool {
+	// Early check: daemon requires a git repository (unless --local mode)
+	// Skip attempting to start and avoid the 5-second wait if not in git repo
+	if !isGitRepo() {
+		debugLog("not in a git repository, skipping daemon start")
+		fmt.Fprintf(os.Stderr, "%s No git repository initialized - running without background sync\n", ui.RenderMuted("Note:"))
+		return false
+	}
+
 	binPath, err := executableFn()
 	if err != nil {
 		binPath = os.Args[0]