refactor: compact pill-based filter toolbar

Merge the toggleable multi-line FilterBar and the separate ActiveFilterChips
strip into a single always-visible row of pills. Each filter category is a
pill that opens a small popover with its underlying control; when active, the
pill shows its current value inline (so the chips strip is redundant).

- New FilterPill primitive: outside-click + Escape to close, optional inline
  X to clear without opening the popover.
- FilterBar rebuilt out of pills for Date/Type/Rating/Color/Flag/Tags/Sort,
  with a Clear-all pill on the right when any filter is active.
- Drop filterBarOpen from filterStore, the SlidersHorizontal toggle from
  TopBar, the \\ shortcut from useKeyboardShortcuts, and the matching hint
  from KeyboardHints — the bar is always visible now.
- Delete ActiveFilterChips; its information lives inside the pills.

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

frontend/src/store/filterStore.ts

@@ -43,8 +43,6 @@ export interface FilterState {
 export const ALL_PHOTOS_SECTION = 'all-photos'
 
 interface FilterStore extends FilterState {
-  filterBarOpen: boolean
-
   /** The active section id. Changes via navigateToSection. */
   currentSection: string
   /** Per-section snapshot of filter state, in-memory. Restored on return. */
@@ -72,9 +70,6 @@ interface FilterStore extends FilterState {
   setSortOrder: (order: SortOrder) => void
   toggleSortOrder: () => void
 
-  setFilterBarOpen: (open: boolean) => void
-  toggleFilterBar: () => void
-
   /** Navigate to a section. Saves the current section's filter state into
    *  the in-memory map under the OLD section id, then loads the saved
    *  state for the destination — or, if none exists, applies the preset
@@ -132,7 +127,6 @@ function snapshotFilters(s: FilterState): FilterState {
 
 export const useFilterStore = create<FilterStore>((set) => ({
   ...INITIAL_FILTERS,
-  filterBarOpen: false,
   currentSection: ALL_PHOTOS_SECTION,
   sectionFilters: {},
   sectionPresets: { [ALL_PHOTOS_SECTION]: {} },
@@ -165,9 +159,6 @@ export const useFilterStore = create<FilterStore>((set) => ({
   toggleSortOrder: () =>
     set((s) => ({ sortOrder: s.sortOrder === 'desc' ? 'asc' : 'desc' })),
 
-  setFilterBarOpen: (filterBarOpen) => set({ filterBarOpen }),
-  toggleFilterBar: () => set((s) => ({ filterBarOpen: !s.filterBarOpen })),
-
   navigateToSection: (sectionId, presetOverrides = {}) =>
     set((s) => {
       // Snapshot the current section's filters before switching.