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/interfaces/chat-provider.interface.ts

@@ -76,4 +76,17 @@ export interface IChatProvider {
    * Parse a command from a message
    */
   parseCommand(message: ChatMessage): ChatCommand | null;
+
+  /**
+   * Edit an existing message in a channel.
+   *
+   * Optional method for providers that support message editing
+   * (e.g., Matrix via m.replace, Discord via message.edit).
+   * Used for streaming AI responses with incremental updates.
+   *
+   * @param channelId - The channel/room ID
+   * @param messageId - The original message/event ID to edit
+   * @param content - The updated message content
+   */
+  editMessage?(channelId: string, messageId: string, content: string): Promise<void>;
 }