feat: add /api/messages/images endpoint + ImageGrid fetch

Backend:
- New GET /api/messages/images?guildId=&limit= endpoint
- Queries attachments table for image/* MIME type, returns distinct messages
- Repository uses Drizzle subquery + join pattern

Frontend:
- New get_images() API client function
- ImageGrid fetches from /api/messages/images when Images tab selected
- Separate image_messages signal, fetched on tab switch

Deploy: hot-patched JS/WASM files to running containers

services/backend/src/modules/messages/messages.routes.ts

@@ -4,6 +4,7 @@ import express from "express";
 import { asyncHandler } from "../../shared/middlewares/index.js";
 import {
   handleGetAttachmentsByChannel,
+  handleGetImageMessages,
   handleGetMessageById,
   handleGetMessagesByChannel,
   handleListMessages,
@@ -31,6 +32,11 @@ const reanalyzeBatchInFlight = new Set<string>();
 export function createMessagesRouter(): Router {
   const router = express.Router();
 
+  // GET /api/messages/images - Get messages with image attachments
+  // MUST be registered BEFORE /messages/:channelId so "images" is not
+  // captured as a channelId param.
+  router.get("/messages/images", handleGetImageMessages);
+
   // GET /api/messages - List messages
   router.get("/messages", handleListMessages);