feat: refactor grouping views into card-grid browse pattern

Replace Timeline-based grouped views (tags, colors, rated) with
dedicated card-grid components that drill into Timeline detail views
on click/Enter. Adds shared useCardGridNav hook for arrow-key
navigation across all four card grids (tags, colors, rated, people).

- TagsView, ColorsView, RatedView: card grid → inline Timeline detail
- PeopleView: migrated to same pattern (Timeline replaces custom grid)
- Tags endpoint: fall back to first associated photo for representative
- Filter store: add ratingMax for exact rating filtering in RatedView
- Timeline: remove tag/rating/color grouping; skip date headers when
  groupBy != 'date' so detail views render flat grids
- SettingsDialog: bump z-index above Leaflet map layers

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -3,6 +3,9 @@ import { Timeline } from './components/timeline/Timeline'
 import { DuplicatesView } from './components/duplicates/DuplicatesView'
 import { MapView } from './components/map/MapView'
 import { PeopleView } from './components/people/PeopleView'
+import { TagsView } from './components/tags/TagsView'
+import { ColorsView } from './components/colors/ColorsView'
+import { RatedView } from './components/rated/RatedView'
 import { LeftSidebar } from './components/layout/LeftSidebar'
 import { RightSidebar } from './components/layout/RightSidebar'
 import { TopBar } from './components/layout/TopBar'
@@ -89,6 +92,12 @@ function App() {
               <DuplicatesView />
             ) : currentSection === 'people' ? (
               <PeopleView />
+            ) : currentSection === 'tags' ? (
+              <TagsView />
+            ) : currentSection === 'colors' ? (
+              <ColorsView />
+            ) : currentSection === 'rated' ? (
+              <RatedView />
             ) : (
               <Timeline />
             )}