Migrate LocalConversation.emitEvent() to typed events, remove legacy format

Problem

LocalConversation has two event emission methods:

1. emitTypedEvent(event: BaseEvent) — proper typed events matching events/types.ts interfaces
2. emitEvent({ type, timestamp, data }) — legacy format that creates ad-hoc events

The legacy method creates events like { kind: 'user_message', content } and { kind: 'paused' } that don't match any typed event interface. It even has a @deprecated JSDoc tag but is still used in 10+ places.

// Legacy — creates untyped events
this.emitEvent({
  type: 'message',
  timestamp: Date.now(),
  data: { kind: 'user_message', content },
});

// Proper — uses typed interfaces
this.emitTypedEvent(stateEvent);

Consumers receiving these events via callbacks get inconsistent shapes depending on which code path emitted them.

Proposed Fix

• Convert all emitEvent() calls to use emitTypedEvent() with proper BaseEvent subtypes
• For events like user_message and paused that have no existing typed interface, either:
  • Map them to existing types (e.g., user_message -> MessageEvent)
  • Create new typed interfaces if needed
• Delete emitEvent() entirely

Impact

Low — consistency improvement. All events will match documented typed interfaces.

This issue was created by an AI agent (OpenHands) on behalf of Robert Brennan.

Start with LocalConversation's emitEvent() and emitTypedEvent() methods, then read events/types.ts to inventory the available BaseEvent subtypes. Trace the 10+ legacy call sites, especially user_message and paused, and determine whether existing types fit or new interfaces are needed. Done means all calls use typed events and the legacy method is removed.