feat(search): "Pinned only" filter (composes with msgtype + local results)

Adds a "Pinned" toggle chip that narrows results to messages currently in
their room's m.room.pinned_events. Client-side post-filter mirroring the
has:image/file/video pattern: a pure filterGroupsByPinned(groups, enabled,
isPinned) helper consumes a predicate; MessageSearch builds a per-room
Map<roomId, Set<eventId>> from StateEvent.RoomPinnedEvents.

Review fix: the msgtype + pinned filters are now applied to BOTH the server
results AND the encrypted/local-cache results (via a shared applyResultFilters
useCallback), so the chips narrow the whole UI consistently — previously the
local/E2EE section bypassed them.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/features/message-search/useMessageSearch.ts

@@ -51,6 +51,26 @@ export const filterGroupsByMsgType = (
     .filter((group) => group.items.length > 0);
 };
 
+/**
+ * Filter result groups to items whose event is currently pinned in its room.
+ * `isPinned(roomId, eventId)` returns whether the event is in the room's
+ * `m.room.pinned_events` set. When `enabled` is false, groups are returned
+ * unchanged. Now-empty groups are dropped.
+ */
+export const filterGroupsByPinned = (
+  groups: ResultGroup[],
+  enabled: boolean,
+  isPinned: (roomId: string, eventId: string) => boolean,
+): ResultGroup[] => {
+  if (!enabled) return groups;
+  return groups
+    .map((group) => ({
+      ...group,
+      items: group.items.filter((item) => isPinned(group.roomId, item.event.event_id)),
+    }))
+    .filter((group) => group.items.length > 0);
+};
+
 const groupSearchResult = (results: ISearchResult[]): ResultGroup[] => {
   const groups: ResultGroup[] = [];