refactor(backend): remove auth for public API

- Remove auth module (auth.routes.ts, /api/auth/login)
- Remove adminAuth middleware from voice and media routes
- Remove adminAuth() function from shared middlewares
- Remove auth-related e2e test
- Clean up .env.example

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

@@ -1,36 +0,0 @@
-import { UnauthorizedError } from "@bete/shared/errors";
-import { createChildLogger } from "@bete/shared/logger";
-import type { Request, Response, Router } from "express";
-import express from "express";
-import { config } from "../../shared/config/index.js";
-import { asyncHandler, rateLimit } from "../../shared/middlewares/index.js";
-
-const logger = createChildLogger("auth.routes");
-
-const adminPassword = config.ADMIN_PASSWORD || "admin";
-
-// Rate limit: max 10 login attempts per IP per 15 minutes
-const loginRateLimit = rateLimit({ windowMs: 15 * 60 * 1000, max: 10 });
-
-export function createAuthRouter(): Router {
-  const router = express.Router();
-
-  // POST /api/auth/login
-  router.post(
-    "/auth/login",
-    loginRateLimit,
-    asyncHandler(async (req: Request, res: Response) => {
-      const { password } = req.body as { password?: string };
-
-      logger.debug("Auth login attempt");
-
-      if (!password || password !== adminPassword) {
-        throw new UnauthorizedError("Invalid password");
-      }
-
-      res.json({ ok: true });
-    }),
-  );
-
-  return router;
-}