feat: add EditEventScreen with calendar and chat mode support

Add a unified event editor that works in two modes:
- Calendar mode: Create/edit events directly via EventService API
- Chat mode: Edit AI-proposed events before confirming them

The chat mode allows users to modify proposed events (title, time,
recurrence) and persists changes both locally and to the server.

New components: DateTimePicker, ScrollableDropdown, useDropdownPosition
New API: PUT /api/chat/messages/:messageId/proposal

apps/client/package.json

@@ -14,6 +14,7 @@
   "dependencies": {
     "@calchat/shared": "*",
     "@expo/vector-icons": "^15.0.3",
+    "@react-native-community/datetimepicker": "8.4.4",
     "@react-navigation/bottom-tabs": "^7.4.0",
     "@react-navigation/elements": "^2.6.3",
     "@react-navigation/native": "^7.1.8",
@@ -43,6 +44,7 @@
     "react-native-screens": "~4.16.0",
     "react-native-web": "~0.21.0",
     "react-native-worklets": "0.5.1",
+    "rrule": "^2.8.1",
     "zustand": "^5.0.9"
   },
   "devDependencies": {