feat: discard view with restore and empty actions

Adds the destructive-action loop the discard concept needed:

- Click "Discarded" in the left sidebar → activates the discarded
  filter; the timeline reloads showing discarded photos.
- DiscardActionBar appears at the top of the timeline only when the
  discarded filter is active. Shows the count, a Restore button (when
  photos are selected), and an Empty discard pile button.
- Empty action goes through a ConfirmDialog (new tiny reusable modal,
  same overlay pattern as AddSourceFolderDialog).
- Restore goes through POST /api/v1/discard/restore.
- DELETE /api/v1/discard/empty now actually os.unlink()s the files
  from disk in addition to removing the DB rows. Per-file failures
  are logged and reported in the response so a single permission
  error doesn't abort the batch.

Other library nodes wired in passing:
- "All Photos"   → clearAll()
- "Rated"        → setRatingMin(1)
- "Flagged"      → setFlag('picked')
- "Discarded"    → setFlag('discarded')
- "By Date"      left unwired (needs a date-grouping UI)

Single-photo restore via the U keyboard shortcut already worked from
an earlier round, no change needed.

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

frontend/src/components/dialogs/ConfirmDialog.tsx

@@ -0,0 +1,75 @@
+import { useEffect } from 'react'
+import clsx from 'clsx'
+
+interface ConfirmDialogProps {
+  isOpen: boolean
+  title: string
+  message: React.ReactNode
+  confirmLabel?: string
+  cancelLabel?: string
+  /** When true, the confirm button uses the destructive accent. */
+  destructive?: boolean
+  onConfirm: () => void
+  onClose: () => void
+}
+
+/**
+ * Tiny modal-confirmation dialog. Mirrors the AddSourceFolderDialog overlay
+ * pattern (custom fixed inset-0 backdrop, no shadcn Dialog dep). Esc closes.
+ */
+export function ConfirmDialog({
+  isOpen,
+  title,
+  message,
+  confirmLabel = 'Confirm',
+  cancelLabel = 'Cancel',
+  destructive = false,
+  onConfirm,
+  onClose,
+}: ConfirmDialogProps) {
+  // Esc to close.
+  useEffect(() => {
+    if (!isOpen) return
+    const handler = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') onClose()
+    }
+    window.addEventListener('keydown', handler)
+    return () => window.removeEventListener('keydown', handler)
+  }, [isOpen, onClose])
+
+  if (!isOpen) return null
+
+  return (
+    <div className="fixed inset-0 z-50">
+      <div
+        className="absolute inset-0 bg-black/60 backdrop-blur-sm"
+        onClick={onClose}
+      />
+      <div className="absolute left-1/2 top-1/2 -translate-x-1/2 -translate-y-1/2">
+        <div className="relative z-10 w-96 rounded-lg border border-border bg-surface p-5 shadow-2xl">
+          <h2 className="mb-2 text-base font-semibold text-text">{title}</h2>
+          <div className="mb-4 text-sm text-text-muted">{message}</div>
+          <div className="flex justify-end gap-2">
+            <button
+              onClick={onClose}
+              className="rounded border border-border px-3 py-1.5 text-sm text-text hover:bg-surface-2"
+            >
+              {cancelLabel}
+            </button>
+            <button
+              onClick={onConfirm}
+              className={clsx(
+                'rounded px-3 py-1.5 text-sm font-medium text-white',
+                destructive
+                  ? 'bg-reject hover:bg-reject/80'
+                  : 'bg-primary hover:bg-primary/80'
+              )}
+            >
+              {confirmLabel}
+            </button>
+          </div>
+        </div>
+      </div>
+    </div>
+  )
+}

frontend/src/components/discard/DiscardActionBar.tsx

@@ -0,0 +1,112 @@
+import { useState } from 'react'
+import { RotateCcw, Trash2 } from 'lucide-react'
+import { useMutation, useQueryClient } from '@tanstack/react-query'
+import { usePhotoStore } from '../../store/photoStore'
+import { useFilterStore } from '../../store/filterStore'
+import { usePhotosQuery } from '../../hooks/usePhotosQuery'
+import { discard as discardApi } from '../../services/api'
+import { toast } from '../ToastContainer'
+import { ConfirmDialog } from '../dialogs/ConfirmDialog'
+
+/**
+ * Top-of-timeline bar visible only when the discarded filter is active.
+ * Shows a count, lets the user restore the current selection, and lets them
+ * permanently empty the discard pile (with confirmation).
+ */
+export function DiscardActionBar() {
+  const flag = useFilterStore((s) => s.flag)
+  const selectedPhotos = usePhotoStore((s) => s.selectedPhotos)
+  const clearSelection = usePhotoStore((s) => s.clearSelection)
+  const queryClient = useQueryClient()
+  const { data: photos = [] } = usePhotosQuery()
+
+  const [confirmOpen, setConfirmOpen] = useState(false)
+
+  const restoreMutation = useMutation({
+    mutationFn: (ids: string[]) => discardApi.restore(ids),
+    onSuccess: (_, ids) => {
+      toast.success('Restored', `${ids.length} photo${ids.length > 1 ? 's' : ''} restored`)
+      clearSelection()
+      queryClient.invalidateQueries({ queryKey: ['photos'] })
+    },
+    onError: (e: any) => toast.error('Restore failed', e.message || 'Unknown error'),
+  })
+
+  const emptyMutation = useMutation({
+    mutationFn: () => discardApi.empty(),
+    onSuccess: (data: any) => {
+      const count = data?.deleted ?? 0
+      const errors = data?.file_errors ?? 0
+      if (errors > 0) {
+        toast.error(
+          `Emptied with ${errors} error${errors > 1 ? 's' : ''}`,
+          `${count} record${count > 1 ? 's' : ''} deleted; some files could not be removed`
+        )
+      } else {
+        toast.success('Discard pile emptied', `${count} photo${count > 1 ? 's' : ''} permanently deleted`)
+      }
+      clearSelection()
+      queryClient.invalidateQueries({ queryKey: ['photos'] })
+      setConfirmOpen(false)
+    },
+    onError: (e: any) => toast.error('Empty failed', e.message || 'Unknown error'),
+  })
+
+  if (flag !== 'discarded') return null
+
+  const total = photos.length
+  const selected = selectedPhotos.length
+
+  return (
+    <>
+      <div className="flex items-center justify-between gap-3 border-b border-border bg-reject/10 px-4 py-2 text-sm">
+        <div className="flex items-center gap-2 text-text">
+          <Trash2 className="h-4 w-4 text-reject" />
+          <span className="font-medium">Discarded</span>
+          <span className="text-text-muted">
+            {total} photo{total === 1 ? '' : 's'}
+          </span>
+        </div>
+
+        <div className="flex items-center gap-2">
+          {selected > 0 && (
+            <button
+              onClick={() => restoreMutation.mutate(selectedPhotos)}
+              disabled={restoreMutation.isPending}
+              className="flex items-center gap-1.5 rounded bg-surface-2 px-3 py-1 text-text hover:bg-surface-offset disabled:opacity-50"
+              title="Restore selected (U)"
+            >
+              <RotateCcw className="h-3.5 w-3.5" />
+              Restore {selected}
+            </button>
+          )}
+          <button
+            onClick={() => setConfirmOpen(true)}
+            disabled={total === 0 || emptyMutation.isPending}
+            className="flex items-center gap-1.5 rounded bg-reject/20 px-3 py-1 text-reject hover:bg-reject/30 disabled:opacity-50"
+            title="Permanently delete all discarded photos and files"
+          >
+            <Trash2 className="h-3.5 w-3.5" />
+            Empty discard pile
+          </button>
+        </div>
+      </div>
+
+      <ConfirmDialog
+        isOpen={confirmOpen}
+        title="Empty discard pile?"
+        message={
+          <>
+            This will <strong className="text-text">permanently delete</strong>{' '}
+            {total} photo{total === 1 ? '' : 's'} and remove the file
+            {total === 1 ? '' : 's'} from disk. This cannot be undone.
+          </>
+        }
+        confirmLabel="Empty pile"
+        destructive
+        onConfirm={() => emptyMutation.mutate()}
+        onClose={() => setConfirmOpen(false)}
+      />
+    </>
+  )
+}

frontend/src/components/layout/LeftSidebar.tsx

@@ -18,6 +18,7 @@ import { AddSourceFolderDialog } from '../dialogs/AddSourceFolderDialog'
 import { sourceFolders, library } from '../../services/api'
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
 import { toast } from '../ToastContainer'
+import { useFilterStore } from '../../store/filterStore'
 
 interface TreeItem {
   id: string
@@ -33,8 +34,34 @@ export function LeftSidebar() {
   const [selectedItem, setSelectedItem] = useState<string | null>('all-photos')
   const [showAddFolderDialog, setShowAddFolderDialog] = useState(false)
   const [isScanning, setIsScanning] = useState(false)
-  
+
   const queryClient = useQueryClient()
+  const clearAllFilters = useFilterStore((s) => s.clearAll)
+  const setRatingMin = useFilterStore((s) => s.setRatingMin)
+  const setFlag = useFilterStore((s) => s.setFlag)
+
+  // Map a library tree id to a filter-store mutation. Each "virtual node" in
+  // the library tree is just a saved filter preset.
+  const applyLibraryNode = (id: string) => {
+    switch (id) {
+      case 'all-photos':
+        clearAllFilters()
+        break
+      case 'rated':
+        clearAllFilters()
+        setRatingMin(1)
+        break
+      case 'flagged':
+        clearAllFilters()
+        setFlag('picked')
+        break
+      case 'discarded':
+        clearAllFilters()
+        setFlag('discarded')
+        break
+      // 'by-date' is purely visual until we add a date-grouping UI
+    }
+  }
   
   // Fetch folders from API
   const { data: foldersData, refetch: refetchFolders } = useQuery({
@@ -152,6 +179,8 @@ export function LeftSidebar() {
             setSelectedItem(item.id)
             if (hasChildren) {
               toggleExpanded(item.id)
+            } else {
+              applyLibraryNode(item.id)
             }
           }}
         >