feat(packing): item quantity, bag rename, multi-user bags, save as template

- Add quantity field to packing items (persisted, visible per item)
- Bags are now renamable (click to edit in sidebar)
- Bags support multiple user assignments with avatar display
- New packing_bag_members table for multi-user bag ownership
- Save current packing list as reusable template
- Add bag members API endpoint (PUT /bags/:bagId/members)
- Migration 74: quantity on packing_items, user_id on packing_bags, packing_bag_members table

client/src/api/client.ts

@@ -131,6 +131,8 @@ export const packingApi = {
   getCategoryAssignees: (tripId: number | string) => apiClient.get(`/trips/${tripId}/packing/category-assignees`).then(r => r.data),
   setCategoryAssignees: (tripId: number | string, categoryName: string, userIds: number[]) => apiClient.put(`/trips/${tripId}/packing/category-assignees/${encodeURIComponent(categoryName)}`, { user_ids: userIds }).then(r => r.data),
   applyTemplate: (tripId: number | string, templateId: number) => apiClient.post(`/trips/${tripId}/packing/apply-template/${templateId}`).then(r => r.data),
+  saveAsTemplate: (tripId: number | string, name: string) => apiClient.post(`/trips/${tripId}/packing/save-as-template`, { name }).then(r => r.data),
+  setBagMembers: (tripId: number | string, bagId: number, userIds: number[]) => apiClient.put(`/trips/${tripId}/packing/bags/${bagId}/members`, { user_ids: userIds }).then(r => r.data),
   listBags: (tripId: number | string) => apiClient.get(`/trips/${tripId}/packing/bags`).then(r => r.data),
   createBag: (tripId: number | string, data: { name: string; color?: string }) => apiClient.post(`/trips/${tripId}/packing/bags`, data).then(r => r.data),
   updateBag: (tripId: number | string, bagId: number, data: Record<string, unknown>) => apiClient.put(`/trips/${tripId}/packing/bags/${bagId}`, data).then(r => r.data),