feat: storage watchdog — USB disconnect detection, auto-stop, safe eject, auto-reconnect (v0.17.0)

New storage watchdog monitors registered storage paths every 5s. On disconnect
(3 consecutive probe failures), auto-stops affected apps, lazy-unmounts stale
VFS entries, fires alerts/notifications/hub report. On reconnect (UUID detected),
auto-remounts via fstab, cleans stale restic locks, offers app restart.

Safe disconnect UI for USB drives: confirmation dialog, stop apps, sync, unmount.
Disconnected state visible across all pages (dashboard, settings, backups, monitoring)
with hatched red bars and badges. Backup guards skip disconnected drives.

22 files changed (1 new: monitor/watchdog.go), ~1500 lines added.

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

controller/internal/system/mounts_other.go

@@ -80,3 +80,30 @@ func CheckBackupDestination(path string) DestinationHealth {
 		Severity:   "ok",
 	}
 }
+
+// ProbeStatus represents the result of a storage path probe.
+type ProbeStatus int
+
+const (
+	ProbeConnected    ProbeStatus = iota
+	ProbeDisconnected
+	ProbeTimeout
+)
+
+// ProbeResult holds the outcome of a storage path probe.
+type ProbeResult struct {
+	Status ProbeStatus
+	Err    error
+}
+
+// ProbeStoragePath always returns connected on non-Linux.
+func ProbeStoragePath(_ string) ProbeResult { return ProbeResult{Status: ProbeConnected} }
+
+// IsUSBDevice always returns false on non-Linux.
+func IsUSBDevice(_ string) bool { return false }
+
+// ParseFstabUUID always returns empty on non-Linux.
+func ParseFstabUUID(_, _ string) string { return "" }
+
+// HasFelhomRawMount always returns false on non-Linux.
+func HasFelhomRawMount(_, _ string) (string, bool) { return "", false }