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/report/pusher.go

@@ -35,6 +35,7 @@ type Pusher struct {
 	httpClient *http.Client
 	logger     *log.Logger
 	enabled    bool
+	debug      bool
 
 	statusMu sync.RWMutex
 	status   PushStatus
@@ -45,7 +46,7 @@ type Pusher struct {
 }
 
 // NewPusher creates a new report pusher from hub configuration.
-func NewPusher(cfg *config.HubConfig, logger *log.Logger) *Pusher {
+func NewPusher(cfg *config.HubConfig, logger *log.Logger, debug bool) *Pusher {
 	return &Pusher{
 		hubURL: strings.TrimRight(cfg.URL, "/"),
 		apiKey: cfg.APIKey,
@@ -54,6 +55,7 @@ func NewPusher(cfg *config.HubConfig, logger *log.Logger) *Pusher {
 		},
 		logger:  logger,
 		enabled: cfg.Enabled,
+		debug:   debug,
 	}
 }
 
@@ -69,6 +71,9 @@ func (p *Pusher) Push(report *Report) error {
 	}
 
 	url := p.hubURL + "/api/v1/report"
+	if p.debug {
+		p.logger.Printf("[DEBUG] Push: url=%s payload=%d bytes", url, len(data))
+	}
 
 	p.statusMu.Lock()
 	p.status.LastAttempt = time.Now()
@@ -143,6 +148,9 @@ func (p *Pusher) PushInfraBackup(data []byte) error {
 	}
 
 	url := p.hubURL + "/api/v1/infra-backup"
+	if p.debug {
+		p.logger.Printf("[DEBUG] PushInfraBackup: url=%s payload=%d bytes", url, len(data))
+	}
 
 	var lastErr error
 	for attempt := 0; attempt < 3; attempt++ {
@@ -173,6 +181,9 @@ func (p *Pusher) PushInfraBackup(data []byte) error {
 			return nil
 		}
 		lastErr = fmt.Errorf("HTTP %d", resp.StatusCode)
+		if p.debug {
+			p.logger.Printf("[DEBUG] PushInfraBackup: attempt %d failed — HTTP %d", attempt+1, resp.StatusCode)
+		}
 	}
 
 	return fmt.Errorf("infra backup push failed after 3 attempts: %w", lastErr)