feat: add client-side permission gating to all write-action UIs

Gate all mutating UI elements with useCanDo() permission checks:
- BudgetPanel (budget_edit), PackingListPanel (packing_edit)
- DayPlanSidebar, DayDetailPanel (day_edit)
- ReservationsPanel, ReservationModal (reservation_edit)
- CollabNotes, CollabPolls, CollabChat (collab_edit)
- FileManager (file_edit, file_delete, file_upload)
- PlaceFormModal, PlaceInspector, PlacesSidebar (place_edit, file_upload)
- TripFormModal (trip_edit, trip_cover_upload)
- DashboardPage (trip_edit, trip_cover_upload, trip_delete, trip_archive)
- TripMembersModal (member_manage, share_manage)

Also: fix redundant getTripOwnerId queries in trips.ts, remove dead
getTripOwnerId function, fix TripMembersModal grid when share hidden,
fix canRemove logic, guard TripListItem empty actions div.

client/src/pages/DashboardPage.tsx

@@ -410,7 +410,7 @@ function TripListItem({ trip, onEdit, onDelete, onArchive, onClick, t, locale, i
       </div>
 
       {/* Actions */}
-      {(!!trip.is_owner || isAdmin) && (
+      {(onEdit || onArchive || onDelete) && (
       <div style={{ display: 'flex', gap: 4, flexShrink: 0 }} onClick={e => e.stopPropagation()}>
         {onEdit && <CardAction onClick={() => onEdit(trip)} icon={<Edit2 size={12} />} label="" />}
         {onArchive && <CardAction onClick={() => onArchive(trip.id)} icon={<Archive size={12} />} label="" />}