refactor(backend): flatten module structure, move routes to .routes.ts files

- Remove empty controllers/, services/, repositories/ subdirectories
- Move routes/index.ts into module.routes.ts (flat naming convention)
- Update imports in http/app.ts

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

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

@@ -0,0 +1,14 @@
+import type { Router } from "express";
+import express from "express";
+
+export function createVoiceRouter(): Router {
+  const router = express.Router();
+
+  // TODO: Implement voice routes
+  // GET /api/voice/recordings
+  // GET /api/voice/recordings/:userId
+  // POST /api/voice/connect
+  // POST /api/voice/disconnect
+
+  return router;
+}