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/App.tsx

@@ -8,7 +8,6 @@ import { ToastContainer } from './components/ToastContainer'
 import { KeyboardHints } from './components/KeyboardHints'
 import { PreviewView } from './components/preview/PreviewView'
 import { FilterBar } from './components/filter/FilterBar'
-import { ActiveFilterChips } from './components/filter/ActiveFilterChips'
 import { DiscardActionBar } from './components/discard/DiscardActionBar'
 import { usePhotoStore } from './store/photoStore'
 import { useKeyboardShortcuts } from './hooks/useKeyboardShortcuts'
@@ -52,7 +51,6 @@ function App() {
     <div className="flex flex-col h-screen bg-bg text-text">
       <TopBar />
       <FilterBar />
-      <ActiveFilterChips />
       <DiscardActionBar />
       <KeyboardHints />