Bulk delete, editable share links, gallery filter fix

- shift-click selects ranges in the gallery; selection bar gains
  'Delete N' with a single confirm (POST /api/photos/delete)
- PATCH /api/shares/{id}: allow_download and expiry editable in place,
  token and client feedback preserved
- Gallery: re-attach ResizeObserver via callback ref — after a filter
  with zero matches the gallery stayed blank at width 0

frontend/src/components/SelectionBar.jsx

@@ -15,6 +15,7 @@ export default function SelectionBar({
   onClear,
   onDownload,
   onDownloadAll,
+  onDelete,
 }) {
   if (total === 0) return null
 
@@ -47,6 +48,11 @@ export default function SelectionBar({
       <button className="btn btn-primary" onClick={onDownload}>
         Download {count} as ZIP ({fmtBytes(selectedBytes)})
       </button>
+      {onDelete && (
+        <button className="btn btn-danger" onClick={onDelete}>
+          Delete {count}
+        </button>
+      )}
     </div>
   )
 }