feat(#383): Streaming AI responses via Matrix message edits

- Add MatrixStreamingService with editMessage, setTypingIndicator, streamResponse
- Rate-limited edits (500ms) for incremental streaming output
- Typing indicator management during generation
- Graceful error handling and fallback for non-streaming scenarios
- Add optional editMessage to IChatProvider interface
- Add getClient() accessor to MatrixService for streaming service
- Register MatrixStreamingService in BridgeModule
- Tests: 20 tests pass

Refs #383

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/bridge/matrix/matrix.service.ts

@@ -269,6 +269,18 @@ export class MatrixService implements IChatProvider {
     return this.connected;
   }
 
+  /**
+   * Get the underlying MatrixClient instance.
+   *
+   * Used by MatrixStreamingService for low-level operations
+   * (message edits, typing indicators) that require direct client access.
+   *
+   * @returns The MatrixClient instance, or null if not connected
+   */
+  getClient(): MatrixClient | null {
+    return this.client;
+  }
+
   /**
    * Send a message to a room
    */