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/doctor.go

@@ -349,7 +349,12 @@ func runDiagnostics(path string) doctorResult {
 		result.OverallOK = false
 	}
 
-	// Check 8: Daemon health
+	// Check 8a: Git sync setup (informational - explains why daemon might not start)
+	gitSyncCheck := convertWithCategory(doctor.CheckGitSyncSetup(path), doctor.CategoryRuntime)
+	result.Checks = append(result.Checks, gitSyncCheck)
+	// Don't fail overall check for git sync warning - beads works fine without git
+
+	// Check 8b: Daemon health
 	daemonCheck := convertWithCategory(doctor.CheckDaemonStatus(path, Version), doctor.CategoryRuntime)
 	result.Checks = append(result.Checks, daemonCheck)
 	if daemonCheck.Status == statusWarning || daemonCheck.Status == statusError {