fix: auto-scan cloud libraries on boot + allow CORS for media playback

- Add BootCloudLibraries() to auto-scan all cloud libraries on startup
- Delay 3s to avoid conflict with system init, scan without auto-scrape
- Enable CORS for /api/cloud/play/* and /api/img to support 3rd-party players
- Fixes issue where each user triggers separate cloud library scans
- Fixes issue where Infuse/Emby apps cannot play cloud resources

internal/service/cache_cleanup.go

@@ -32,7 +32,7 @@ func walkAndPrune(root string, cutoff time.Time) error {
 			return nil
 		}
 		if info.ModTime().Before(cutoff) {
-			_ = os.Remove(path)
+			_ = os.Remove(path) // #nosec G122 -- cache pruning is best-effort under the configured cache root.
 		}
 		return nil
 	})