feat(backend): implement all missing endpoints, real analytics queries, and WebSocket server

- Replace stub analytics.repository.ts with real PostgreSQL queries using pg.Pool
- Add /api/guilds, /api/config, /api/auth/login, /api/ui-state (GET/POST)
- Add /api/review, /api/recordings, /api/analysis/search
- Add /api/messages/:id/reanalyze endpoint
- Add /api/analytics/heatmap and /api/analytics/topics
- Implement media routes (stub responses, backend has no Discord voice client)
- Add WebSocket server at /ws with heartbeat and broadcast functions
- Fix analytics route paths to match frontend contract (dual paths for backward compat)
- Export getPool() from database module for raw SQL queries
- Register all new routers in app.ts

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -0,0 +1,16 @@
+import type { Router } from "express";
+import express from "express";
+import { config } from "../../shared/config/index.js";
+
+export function createConfigRouter(): Router {
+  const router = express.Router();
+
+  // GET /api/config
+  router.get("/config", (_req, res) => {
+    res.json({
+      monitorGuildId: config.MONITOR_GUILD_ID || null,
+    });
+  });
+
+  return router;
+}