feat: safe deletion, album/asset delete, trash, README update

- volume-aware deletion: read-only volumes remove DB only, writable
  volumes soft-delete to trash with configurable grace period
- trash page with restore, worker purge sweep (TRASH_RETENTION_DAYS)
- album delete endpoint + sidebar trash icon
- asset delete from timeline selection toolbar
- all listing queries exclude trashed assets (deleted_at IS NULL)
- timeline ordered by EXIF capture date, date-summary endpoint
- README rewritten with features, setup, full env var table

k-photos-frontend/hooks/use-albums.ts

@@ -36,6 +36,13 @@ export function useAlbums() {
     onSuccess: () => qc.invalidateQueries({ queryKey: ["albums"] }),
   })
 
+  const deleteAlbum = useMutation({
+    mutationFn: async (id: string) => {
+      await api.delete(`/albums/${id}`)
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["albums"] }),
+  })
+
   const addEntry = useMutation({
     mutationFn: async ({ albumId, assetId }: { albumId: string; assetId: string }) => {
       await api.post(`/albums/${albumId}/entries`, { asset_id: assetId })
@@ -60,6 +67,7 @@ export function useAlbums() {
     albums: query.data ?? [],
     isLoading: query.isLoading,
     createAlbum: create.mutateAsync,
+    deleteAlbum: deleteAlbum.mutateAsync,
     updateAlbum: update.mutateAsync,
     addEntry: addEntry.mutateAsync,
     removeEntry: removeEntry.mutateAsync,