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/web/templates/style.css

@@ -2254,6 +2254,41 @@ a.stat-card:hover {
     background: rgba(250, 204, 21, 0.15);
     color: #facc15;
 }
+.badge-error {
+    background: rgba(239, 68, 68, 0.15);
+    color: #ef4444;
+}
+
+/* Disconnected storage path card */
+.storage-disconnected {
+    opacity: 0.75;
+    border-style: dashed;
+}
+.storage-disconnected .storage-disconnected-info {
+    display: flex;
+    flex-direction: column;
+    gap: .25rem;
+}
+.storage-stopped-apps-info {
+    display: flex;
+    align-items: center;
+    flex-wrap: wrap;
+    gap: .25rem;
+    margin-bottom: .5rem;
+}
+
+/* Disconnected bar on dashboard/monitoring */
+.system-bar-disconnected {
+    background: repeating-linear-gradient(
+        -45deg,
+        rgba(239, 68, 68, 0.15),
+        rgba(239, 68, 68, 0.15) 5px,
+        transparent 5px,
+        transparent 10px
+    );
+    height: 100%;
+    border-radius: 4px;
+}
 
 /* Task progress bar (storage init — not disk usage zone gradient) */
 .progress-bar-task {