feat(20): export SubscriptionEvent type from shared package

Add SubscriptionEvent interface for frontend consumption of SSE
subscription data in onData callbacks. Vite proxy confirmed compatible
with SSE streaming (http-proxy passes chunked responses by default).

packages/shared/src/index.ts

@@ -1,2 +1,2 @@
 export type { AppRouter } from './trpc.js';
-export type { Initiative, Phase, Plan, Task, Agent, Message, PendingQuestions, QuestionItem } from './types.js';
+export type { Initiative, Phase, Plan, Task, Agent, Message, PendingQuestions, QuestionItem, SubscriptionEvent } from './types.js';

packages/shared/src/types.ts

@@ -1,2 +1,13 @@
 export type { Initiative, Phase, Plan, Task, Agent, Message } from '../../../src/db/schema.js';
 export type { PendingQuestions, QuestionItem } from '../../../src/agent/types.js';
+
+/**
+ * Shape of events received from tRPC subscription streams.
+ * Used by the frontend in onData callbacks.
+ */
+export interface SubscriptionEvent {
+  id: string;
+  type: string;
+  payload: unknown;
+  timestamp: string;
+}