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/services/interfaces/ChatRepository.ts

@@ -2,6 +2,7 @@ import {
   ChatMessage,
   Conversation,
   CreateMessageDTO,
+  CreateEventDTO,
   GetMessagesOptions,
   UpdateMessageDTO,
 } from "@calchat/shared";
@@ -32,4 +33,10 @@ export interface ChatRepository {
     proposalId: string,
     respondedAction: "confirm" | "reject",
   ): Promise<ChatMessage | null>;
+
+  updateProposalEvent(
+    messageId: string,
+    proposalId: string,
+    event: CreateEventDTO,
+  ): Promise<ChatMessage | null>;
 }