feat: prune orphaned photo rows + retry-pending action

Adds /api/v1/library/maintenance/{missing-stats,prune-missing} backed
by a new cleanup helper that deletes Photo rows whose files no longer
exist on disk under a *mounted* source root. Skips photos under
unmounted roots so a temporarily-disconnected drive doesn't get
silently nuked.

Settings panel surfaces the orphan count with a destructive Prune
button, plus a "Kick pending" action that re-queues photos stuck in
processing_status='pending' (typically left behind when the scanner
created the row but the worker never picked up the thumbnail task).

Common trigger: PHOTO_DIRS in .env was repointed at a different
library root, leaving every old row dangling.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/dialogs/SettingsDialog.tsx

@@ -19,6 +19,7 @@ import {
   type LibraryStats,
   type MediaType,
   type WorkerStatus,
+  type MissingStats,
 } from '../../services/api'
 import { toast } from '../ToastContainer'
 
@@ -42,6 +43,7 @@ export function SettingsDialog({ isOpen, onClose }: SettingsDialogProps) {
   const [thumbStats, setThumbStats] = useState<ThumbnailStats | null>(null)
   const [libStats, setLibStats] = useState<LibraryStats | null>(null)
   const [workerStatus, setWorkerStatus] = useState<WorkerStatus | null>(null)
+  const [missingStats, setMissingStats] = useState<MissingStats | null>(null)
   const [loadingStats, setLoadingStats] = useState(false)
   const [loadingWorkers, setLoadingWorkers] = useState(false)
   const [showAllErrors, setShowAllErrors] = useState(false)
@@ -69,8 +71,12 @@ export function SettingsDialog({ isOpen, onClose }: SettingsDialogProps) {
   const refreshWorkers = useCallback(async () => {
     setLoadingWorkers(true)
     try {
-      const ws = await library.maintenance.workerStatus()
+      const [ws, ms] = await Promise.all([
+        library.maintenance.workerStatus(),
+        library.maintenance.missingStats(),
+      ])
       setWorkerStatus(ws)
+      setMissingStats(ms)
     } catch (e) {
       console.error('Failed to load worker status', e)
       toast.error('Could not load worker status')
@@ -111,7 +117,7 @@ export function SettingsDialog({ isOpen, onClose }: SettingsDialogProps) {
       try {
         const result = await fn()
         toast.success(successTitle, describe?.(result))
-        await refreshStats()
+        await Promise.all([refreshStats(), refreshWorkers()])
       } catch (e: unknown) {
         const message = e instanceof Error ? e.message : String(e)
         toast.error(`${successTitle} failed`, message)
@@ -119,11 +125,18 @@ export function SettingsDialog({ isOpen, onClose }: SettingsDialogProps) {
         setBusy((b) => ({ ...b, [key]: false }))
       }
     },
-    [busy, refreshStats]
+    [busy, refreshStats, refreshWorkers]
   )
 
   const regenerate = useCallback(
-    (key: string, body: { media_types?: MediaType[]; only_failed?: boolean }) =>
+    (
+      key: string,
+      body: {
+        media_types?: MediaType[]
+        only_failed?: boolean
+        only_pending?: boolean
+      }
+    ) =>
       runAction(
         key,
         () => library.maintenance.regenerateThumbnails(body),
@@ -263,6 +276,18 @@ export function SettingsDialog({ isOpen, onClose }: SettingsDialogProps) {
                   {thumbStats ? ` (${thumbStats.failed})` : ''}
                 </ActionButton>
 
+                <ActionButton
+                  loading={busy['regen-pending']}
+                  onClick={() =>
+                    regenerate('regen-pending', { only_pending: true })
+                  }
+                  disabled={!!thumbStats && thumbStats.pending === 0}
+                >
+                  <RefreshCw className="h-4 w-4" />
+                  Kick pending
+                  {thumbStats ? ` (${thumbStats.pending})` : ''}
+                </ActionButton>
+
                 <ActionButton
                   loading={busy['regen-all']}
                   destructive
@@ -394,6 +419,54 @@ export function SettingsDialog({ isOpen, onClose }: SettingsDialogProps) {
                 </div>
               )}
 
+              {/* Orphaned rows (files gone from disk) */}
+              {missingStats && (missingStats.would_delete ?? 0) > 0 && (
+                <div className="mt-3 rounded border border-star/40 bg-star/10 p-2">
+                  <div className="flex items-center justify-between gap-2">
+                    <div className="text-xs">
+                      <div className="flex items-center gap-1.5 font-medium text-text">
+                        <AlertTriangle className="h-3.5 w-3.5 text-star" />
+                        {missingStats.would_delete} orphaned photo rows
+                      </div>
+                      <div className="mt-0.5 text-[10px] text-text-muted">
+                        Files no longer exist on disk under a mounted source
+                        root. Usually means PHOTO_DIRS was repointed at a
+                        different library.
+                        {missingStats.skipped_unmounted > 0 && (
+                          <>
+                            {' '}
+                            {missingStats.skipped_unmounted} more rows are
+                            under unmounted roots and will not be touched.
+                          </>
+                        )}
+                      </div>
+                    </div>
+                    <ActionButton
+                      loading={busy['prune-missing']}
+                      destructive
+                      onClick={() => {
+                        if (
+                          !confirm(
+                            `Delete ${missingStats.would_delete} photo rows whose files are missing? ` +
+                              'This cannot be undone.'
+                          )
+                        )
+                          return
+                        runAction(
+                          'prune-missing',
+                          () => library.maintenance.pruneMissing(),
+                          'Orphans pruned',
+                          (r) => `${r.deleted ?? 0} rows deleted`
+                        )
+                      }}
+                    >
+                      <AlertTriangle className="h-4 w-4" />
+                      Prune
+                    </ActionButton>
+                  </div>
+                </div>
+              )}
+
               {/* Per-worker breakdown */}
               {workerStatus && workerStatus.workers.length > 0 && (
                 <div className="mt-3 space-y-2">