feat(topbar): drop search box to reclaim filter-bar space

The search box on the right edge of the filter bar wasn't pulling its
weight — kills it entirely along with the supporting plumbing:

- FilterBar: remove input + Search icon import + local/debounced state
- filterStore: drop `q`, `setQ`, plus all references in INITIAL_FILTERS,
  filtersToParams, hasActiveFilters, snapshotFilters
- usePhotosQuery: stop passing q through filtersToParams
- useFilterUrlSync: drop the `q` URL param read/write
- PhotoThumbnail + PreviewView: remove the search-match banner/chip and
  findSearchMatch helper imports
- Timeline + MemoriesView: stop subscribing to / forwarding the prop
- useKeyboardShortcuts: drop the `/` and Cmd+F focus hotkeys
- KeyboardHints: drop the `/` hint and the now-stale `?` collision note
- delete hooks/useSearchQuery.ts (no callers) and lib/searchMatch.ts

Backend /photos/search endpoint left untouched — no UI reaches it now.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/hooks/usePhotosQuery.ts

@@ -49,7 +49,6 @@ export function usePhotosQuery() {
   const filterParams = useFilterStore(
     useShallow((s) =>
       filtersToParams({
-        q: s.q,
         dateFrom: s.dateFrom,
         dateTo: s.dateTo,
         mediaTypes: s.mediaTypes,