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/setup/scanner.go

@@ -45,7 +45,7 @@ type lsblkDevice struct {
 }
 
 // ScanDrivesForInfraBackups scans all block devices for .felhom-infra-backup/ directories.
-func ScanDrivesForInfraBackups(logger *log.Logger) ([]DriveBackup, error) {
+func ScanDrivesForInfraBackups(logger *log.Logger, debug bool) ([]DriveBackup, error) {
 	logger.Printf("[INFO] Setup: scanning drives for infra backups...")
 
 	// Read currently mounted filesystems
@@ -68,6 +68,10 @@ func ScanDrivesForInfraBackups(logger *log.Logger) ([]DriveBackup, error) {
 		return nil, fmt.Errorf("parsing lsblk: %w", err)
 	}
 
+	if debug {
+		logger.Printf("[DEBUG] Setup scan: lsblk returned %d block devices", len(lsblk.Blockdevices))
+	}
+
 	var results []DriveBackup
 
 	// Flatten all partitions
@@ -83,6 +87,10 @@ func ScanDrivesForInfraBackups(logger *log.Logger) ([]DriveBackup, error) {
 		}
 	}
 
+	if debug {
+		logger.Printf("[DEBUG] Setup scan: found %d partitions to check, %d root devices to skip", len(partitions), len(rootDevices))
+	}
+
 	for _, part := range partitions {
 		// Skip partitions without filesystem
 		if part.FSType == nil || *part.FSType == "" || *part.FSType == "swap" {
@@ -256,7 +264,7 @@ func countValid(results []DriveBackup) int {
 
 // runDriveScan runs the scan asynchronously and stores results on the Server.
 func (s *Server) runDriveScan() {
-	results, err := ScanDrivesForInfraBackups(s.logger)
+	results, err := ScanDrivesForInfraBackups(s.logger, s.isDebug())
 
 	s.scanMu.Lock()
 	defer s.scanMu.Unlock()