fix(mobile): account for bottom navbar in overlays and improve system notices UX

- Add paddingBottom: var(--bottom-nav-h) to all mobile overlays that were
  clipping content behind the bottom navbar: EntryEditor, SystemNoticeModal,
  JourneyPage create modal, TodoListPanel sheets, TripPlannerPage
  PlaceInspector, PackingListPanel bag modal, both PhotoLightboxes,
  FileManager viewer, and shared Modal primitive
- Replace single-notice mobile bottom sheet with a 3-slot horizontal strip
  so adjacent notices are physically present during drag
- Add live-follow swipe left/right to navigate between notices with
  spring-back when under threshold and flushSync to eliminate blink on commit
- Add live-follow swipe down to dismiss all notices with spring-back;
  backdrop tap also triggers the slide-down animation
- Normalize notice height with useLayoutEffect minHeight on strip and
  align-items: stretch so all slots are always the tallest notice height
- Pin CTA button at consistent Y across notices via flex-1 + mt-auto;
  always render invisible Not now placeholder to equalise CTA section height
- Move pager dots/counter below CTA buttons

client/src/components/Files/FileManager.tsx

@@ -94,7 +94,7 @@ function ImageLightbox({ files, initialIndex, onClose }: ImageLightboxProps) {
 
   return (
     <div
-      style={{ position: 'fixed', inset: 0, background: 'rgba(0,0,0,0.92)', zIndex: 2000, display: 'flex', flexDirection: 'column' }}
+      style={{ position: 'fixed', inset: 0, background: 'rgba(0,0,0,0.92)', zIndex: 2000, display: 'flex', flexDirection: 'column', paddingBottom: 'var(--bottom-nav-h)' }}
       onClick={onClose}
       onTouchStart={e => setTouchStart(e.touches[0].clientX)}
       onTouchEnd={e => {