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/Journey/PhotoLightbox.tsx

@@ -69,6 +69,7 @@ export default function PhotoLightbox({ photos, startIndex = 0, onClose }: Props
         position: 'fixed', inset: 0, zIndex: 500,
         background: 'rgba(0,0,0,0.92)', backdropFilter: 'blur(20px)',
         display: 'flex', flexDirection: 'column',
+        paddingBottom: 'var(--bottom-nav-h)',
       }}
       onTouchStart={onTouchStart}
       onTouchEnd={onTouchEnd}