refactor: merge reject into trash as a single soft-trash concept

The Photo model previously had two near-identical "negative culling"
states: is_rejected (a flag) and is_trashed (a flag plus a file move).
Lightroom users typically use one or the other, never both, and the
file-move semantics of the old trash made it harder to undo. Merging
into a single soft is_trashed flag — file stays on disk, restore is a
flag flip, permanent deletion still happens via DELETE /trash/empty.

Backend
- Drop is_rejected from PhotoBase, PhotoResponse, PhotoUpdate, the
  list endpoint filter, and the bulk-action 'reject' branch.
- Add is_trashed to PhotoUpdate so the PATCH path can set it.
- Drop is_rejected Column declaration from the SQLAlchemy model. The
  legacy DB column may persist on existing installs but is no longer
  read or written; SQLAlchemy ignores extra columns.
- Rewrite DELETE /photos/{id} as a soft trash: just sets is_trashed=
  true and trashed_at=now, no shutil.move. Permanent deletion still
  goes through the trash router.

Frontend
- Photo TS type drops is_rejected, gains is_trashed.
- X keyboard shortcut now sets is_trashed=true (was is_rejected); U
  clears both is_picked and is_trashed.
- RightSidebar Reject button → Trash button (Trash2 icon).
- PhotoThumbnail flag overlay shows Trash2 icon for trashed photos
  instead of an X for rejected.
- KeyboardHints relabels X from "Reject" to "Trash".
- filterStore FlagFilter renames 'rejected' → 'trashed'; the params
  builder now sends is_trashed=true for the trashed filter (the list
  endpoint defaults to hiding trashed photos otherwise).
- FilterBar dropdown / URL sync allow-list updated accordingly.

No data migration: existing rejected photos remain as-is (flag stale)
and effectively become unflagged in the new model. Re-trash from the
UI to bring them into the new state.

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

frontend/src/components/layout/RightSidebar.tsx

@@ -9,6 +9,7 @@ import {
   ChevronDown,
   ChevronRight,
   Check,
+  Trash2,
 } from 'lucide-react'
 import clsx from 'clsx'
 import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
@@ -26,7 +27,7 @@ interface PhotoDetails {
   taken_at: string | null
   rating: number
   is_picked: boolean
-  is_rejected: boolean
+  is_trashed: boolean
   exif_json: string | null
 }
 
@@ -107,7 +108,7 @@ export function RightSidebar() {
     mutationFn: (data: {
       rating?: number
       is_picked?: boolean
-      is_rejected?: boolean
+      is_trashed?: boolean
     }) => photosApi.update(activePhotoId!, data),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['photo', activePhotoId] })
@@ -131,7 +132,7 @@ export function RightSidebar() {
   const multipleSelected = selectedPhotos.length > 1
   const rating = photo?.rating ?? 0
   const isPicked = photo?.is_picked ?? false
-  const isRejected = photo?.is_rejected ?? false
+  const isTrashed = photo?.is_trashed ?? false
 
   return (
     <div className="flex h-full flex-col bg-surface">
@@ -186,7 +187,7 @@ export function RightSidebar() {
                 onClick={() =>
                   updateMutation.mutate({
                     is_picked: !isPicked,
-                    is_rejected: false,
+                    is_trashed: false,
                   })
                 }
                 className={clsx(
@@ -202,19 +203,19 @@ export function RightSidebar() {
               <button
                 onClick={() =>
                   updateMutation.mutate({
-                    is_rejected: !isRejected,
+                    is_trashed: !isTrashed,
                     is_picked: false,
                   })
                 }
                 className={clsx(
                   'flex items-center gap-1 rounded px-2 py-1 text-sm transition-colors',
-                  isRejected
+                  isTrashed
                     ? 'bg-reject/20 text-reject'
                     : 'bg-surface-2 text-text-muted hover:bg-surface-offset'
                 )}
               >
-                <X className="h-3 w-3" />
-                Reject
+                <Trash2 className="h-3 w-3" />
+                Trash
               </button>
             </div>
           </div>