Record sent chats in messages repo and blur gallery by default

Threads MessagesRepository through ChatService so first outgoing chat
messages are persisted for stats, and extends the repo + DB client to
support chat-room-keyed lookups. Adds tests covering the new behavior.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/services/response-checker.ts

@@ -56,7 +56,7 @@ export class ResponseCheckerService {
           this.messagesRepo.markGotResponse(message.id);
 
           // Get the original post info
-          const post = this.postsRepo.getById(message.postId);
+          const post = message.postId ? this.postsRepo.getById(message.postId) : undefined;
 
           // Store as successful message for learning
           this.successfulMessagesRepo.insert({