Participants, context menus, budget rename, file types, UI polish

- Assignment participants: toggle who joins each activity
  - Chips with hover-to-remove (strikethrough effect)
  - Add button with dropdown for available members
  - Avatars in day plan sidebar
  - Side-by-side with reservation in place inspector
- Right-click context menus for places, notes in day plan + places list
- Budget categories can now be renamed (pencil icon inline edit)
- Admin: configurable allowed file types (stored in app_settings)
- File manager shows allowed types dynamically
- Hotel picker: select place + save button (no auto-close)
- Edit pencil opens full hotel popup with all options
- Place inspector: opening hours + files side by side on desktop
- Address clamped to 2 lines, coordinates hidden on mobile
- Category shows icon only on mobile
- Rating hidden on mobile in place inspector
- Time validation: "10" becomes "10:00"
- Climate weather: full hourly data from archive API
- CustomSelect: grouped headers support (isHeader)
- Various responsive fixes

client/src/api/client.js

@@ -95,6 +95,8 @@ export const assignmentsApi = {
   reorder: (tripId, dayId, orderedIds) => apiClient.put(`/trips/${tripId}/days/${dayId}/assignments/reorder`, { orderedIds }).then(r => r.data),
   move: (tripId, assignmentId, newDayId, orderIndex) => apiClient.put(`/trips/${tripId}/assignments/${assignmentId}/move`, { new_day_id: newDayId, order_index: orderIndex }).then(r => r.data),
   update: (tripId, dayId, id, data) => apiClient.put(`/trips/${tripId}/days/${dayId}/assignments/${id}`, data).then(r => r.data),
+  getParticipants: (tripId, id) => apiClient.get(`/trips/${tripId}/assignments/${id}/participants`).then(r => r.data),
+  setParticipants: (tripId, id, userIds) => apiClient.put(`/trips/${tripId}/assignments/${id}/participants`, { user_ids: userIds }).then(r => r.data),
 }
 
 export const packingApi = {