feat: drive migration & Tier 2 restic deprecation (v0.18.0)

Phase 1: Deprecate restic as Tier 2 method (rsync only), auto-migrate on startup
Phase 2: Enhanced per-app migration with backup awareness, DB dump copy, auto-cleanup
Phase 3: Full drive migration with decommissioned state, rollback support, wizard UI
Phase 4: Hub report includes decommissioned drive state

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

controller/internal/monitor/watchdog.go

@@ -133,6 +133,11 @@ func (w *StorageWatchdog) Check(ctx context.Context) error {
 		}
 		state.lastProbeTime = time.Now()
 
+		// Skip decommissioned drives entirely — no apps reference them
+		if sp.Decommissioned {
+			continue
+		}
+
 		if sp.Disconnected {
 			w.handleReconnectCheck(ctx, sp)
 		} else {
@@ -434,6 +439,9 @@ func (w *StorageWatchdog) SafeDisconnect(ctx context.Context, path string) (stop
 	if sp.Disconnected {
 		return nil, fmt.Errorf("drive already disconnected")
 	}
+	if sp.Decommissioned {
+		return nil, fmt.Errorf("drive is decommissioned — no apps to stop")
+	}
 
 	label := sp.Label
 	if label == "" {