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/analytics/analytics.routes.ts

@@ -7,7 +7,7 @@ import {
   handleGetOverview,
   handleGetTopViolators,
   handleGetUserLeaderboard,
-} from "../analytics.controller.js";
+} from "./analytics.controller.js";
 
 export function createAnalyticsRouter(): Router {
   const router = express.Router();

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

@@ -1,6 +1,6 @@
 import type { Router } from "express";
 import express from "express";
-import { handleHealthCheck } from "../health.controller.js";
+import { handleHealthCheck } from "./health.controller.js";
 
 export function createHealthRouter(): Router {
   const router = express.Router();

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

@@ -5,7 +5,7 @@ import {
   handleGetMessageById,
   handleGetMessagesByChannel,
   handleListMessages,
-} from "../messages.controller.js";
+} from "./messages.controller.js";
 
 export function createMessagesRouter(): Router {
   const router = express.Router();