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/hooks/useFilterUrlSync.ts

@@ -16,7 +16,7 @@ const ALLOWED_COLORS: ColorLabel[] = [
   'blue',
   'purple',
 ]
-const ALLOWED_FLAGS: FlagFilter[] = ['any', 'picked', 'rejected', 'unflagged']
+const ALLOWED_FLAGS: FlagFilter[] = ['any', 'picked', 'trashed', 'unflagged']
 
 function parseUrl(): Partial<FilterState> {
   const sp = new URLSearchParams(window.location.search)

frontend/src/hooks/useKeyboardShortcuts.ts

@@ -14,7 +14,7 @@ interface KeyboardShortcutsProps {
 interface PhotoUpdate {
   rating?: number
   is_picked?: boolean
-  is_rejected?: boolean
+  is_trashed?: boolean
   color_label?: string | null
 }
 
@@ -129,17 +129,19 @@ export function useKeyboardShortcuts(props: KeyboardShortcutsProps) {
     updateActive({ rating: 0 })
   })
 
-  // Pick / reject / unflag.
+  // Pick / trash / unflag. Trash is the merged "rejected" concept — a soft
+  // flag that hides the photo from the default timeline view; restore via
+  // the trash view (or the U shortcut).
   useHotkeys('p', () => {
-    updateActive({ is_picked: true, is_rejected: false })
+    updateActive({ is_picked: true, is_trashed: false })
   })
 
   useHotkeys('x', () => {
-    updateActive({ is_rejected: true, is_picked: false })
+    updateActive({ is_trashed: true, is_picked: false })
   })
 
   useHotkeys('u', () => {
-    updateActive({ is_picked: false, is_rejected: false })
+    updateActive({ is_picked: false, is_trashed: false })
   })
 
   // Color labels 6-9 (red/orange/yellow/green per spec §6.4).