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/shared/Modal.tsx

@@ -51,7 +51,7 @@ export default function Modal({
   return (
     <div
       className="fixed inset-0 z-[200] flex items-start sm:items-center justify-center px-4 modal-backdrop"
-      style={{ backgroundColor: 'rgba(15, 23, 42, 0.5)', paddingTop: 70, paddingBottom: 20, overflow: 'hidden' }}
+      style={{ backgroundColor: 'rgba(15, 23, 42, 0.5)', paddingTop: 70, paddingBottom: 'calc(20px + var(--bottom-nav-h))', overflow: 'hidden' }}
       onMouseDown={e => { mouseDownTarget.current = e.target }}
       onClick={e => {
         if (e.target === e.currentTarget && mouseDownTarget.current === e.currentTarget) onClose()