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/server/src/repositories/mongo/models/ChatModel.ts

@@ -23,7 +23,6 @@ const EventSchema = new Schema<CreateEventDTO>(
     startTime: { type: Date, required: true },
     endTime: { type: Date, required: true },
     note: { type: String },
-    isRecurring: { type: Boolean },
     recurrenceRule: { type: String },
     exceptionDates: { type: [String] },
   },
@@ -37,7 +36,6 @@ const UpdatesSchema = new Schema<UpdateEventDTO>(
     startTime: { type: Date },
     endTime: { type: Date },
     note: { type: String },
-    isRecurring: { type: Boolean },
     recurrenceRule: { type: String },
   },
   { _id: false },