Add surface.updated to the StreamEventType union in the TS authority

Why: U4 frontend store switches on the event type; the TS union mirrors
the Go EvSurfaceUpdated constant (Core #25) and must include it or the
frontend typecheck rejects the case.

Evidence: go test unchanged (TS-only); frontend tsc in the Dev
workspace after mirror sync.

Impact: Type-only additive.

Refs: Core PR #25; Dev task feature/generative-ui-u4

ts/types.ts

@@ -98,7 +98,8 @@ export type StreamEventType =
   | 'agent.spawn' | 'agent.progress' | 'agent.result'
   | 'artifact.created' | 'artifact.updated'
   | 'run.completed' | 'run.failed' | 'error'
-  | 'card.created' | 'card.updated' | 'card.status' | 'card.resolved';
+  | 'card.created' | 'card.updated' | 'card.status' | 'card.resolved'
+  | 'surface.updated';
 
 export interface StreamEvent<P = unknown> {
   seq: number; runId?: ID; conversationId: ID; ts: string; v: number;