v0.24.0 — Pre-testing observability: debug logging, diagnostic dump, startup self-test

- Add [DEBUG] logging across all modules (backup, storage, sync, selfupdate,
  monitor, notify, report, assets, setup) gated behind logging.level: "debug"
- Add /api/debug/dump endpoint returning full controller state JSON (debug only)
- Add startup self-test validating 9 subsystems (Docker, dirs, storage, hub,
  restic repos, metrics DB) with pass/warn/fail summary
- New packages: internal/selftest, internal/util
- Constructor/signature changes: debug bool params, logger params on
  RunHealthCheck and BuildReport, smart watchdog probe logging

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/assets/syncer.go

@@ -47,12 +47,13 @@ type Syncer struct {
 	fallbackDir string // /usr/share/felhom/assets — baked-in fallback
 	httpClient  *http.Client
 	logger      *log.Logger
+	debug       bool
 	mu          sync.Mutex
 	status      SyncStatus
 }
 
 // New creates a Syncer that downloads assets from the Hub.
-func New(hubURL, apiKey, assetsDir, fallbackDir string, logger *log.Logger) *Syncer {
+func New(hubURL, apiKey, assetsDir, fallbackDir string, logger *log.Logger, debug bool) *Syncer {
 	return &Syncer{
 		hubURL:      strings.TrimSuffix(hubURL, "/"),
 		apiKey:      apiKey,
@@ -60,6 +61,7 @@ func New(hubURL, apiKey, assetsDir, fallbackDir string, logger *log.Logger) *Syn
 		fallbackDir: fallbackDir,
 		httpClient:  &http.Client{Timeout: 60 * time.Second},
 		logger:      logger,
+		debug:       debug,
 		status:      SyncStatus{LastStatus: "never"},
 	}
 }
@@ -78,11 +80,17 @@ func (s *Syncer) Sync(ctx context.Context) error {
 	}
 
 	// 1. Fetch Hub manifest
+	if s.debug {
+		s.logger.Printf("[DEBUG] Asset sync: fetching manifest from %s/api/v1/assets/manifest", s.hubURL)
+	}
 	manifest, err := s.fetchManifest(ctx)
 	if err != nil {
 		s.setError(fmt.Errorf("fetch manifest: %w", err))
 		return err
 	}
+	if s.debug {
+		s.logger.Printf("[DEBUG] Asset sync: manifest has %d files", len(manifest.Files))
+	}
 
 	// 2. Build local hash map
 	localHashes, err := s.buildLocalHashes()
@@ -90,6 +98,9 @@ func (s *Syncer) Sync(ctx context.Context) error {
 		s.setError(fmt.Errorf("scan local assets: %w", err))
 		return err
 	}
+	if s.debug {
+		s.logger.Printf("[DEBUG] Asset sync: %d local files found", len(localHashes))
+	}
 
 	// 3. Download changed/new files
 	hubFiles := make(map[string]bool, len(manifest.Files))
@@ -105,6 +116,9 @@ func (s *Syncer) Sync(ctx context.Context) error {
 			continue
 		}
 
+		if s.debug {
+			s.logger.Printf("[DEBUG] Asset sync: downloading %s (remote sha256=%s)", entry.Filename, entry.SHA256[:12]+"...")
+		}
 		if err := s.downloadFile(ctx, entry.Filename); err != nil {
 			s.logger.Printf("[WARN] Failed to download asset %s: %v", entry.Filename, err)
 			continue
@@ -117,6 +131,9 @@ func (s *Syncer) Sync(ctx context.Context) error {
 	for name := range localHashes {
 		if !hubFiles[name] {
 			path := filepath.Join(s.assetsDir, name)
+			if s.debug {
+				s.logger.Printf("[DEBUG] Asset sync: removing stale file %s", name)
+			}
 			if err := os.Remove(path); err != nil {
 				s.logger.Printf("[WARN] Failed to remove stale asset %s: %v", name, err)
 			} else {