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/shared/middlewares/index.ts

@@ -1,6 +1,5 @@
 import {
   AppError,
-  UnauthorizedError,
   ValidationError,
 } from "@bete/shared/errors";
 import { createChildLogger } from "@bete/shared/logger";
@@ -30,18 +29,6 @@ export function errorHandler(
   });
 }
 
-export function adminAuth(adminPassword: string) {
-  return (req: Request, res: Response, next: NextFunction) => {
-    const password = req.headers["x-admin-password"] as string;
-
-    if (!password || password !== adminPassword) {
-      throw new UnauthorizedError("Invalid admin password");
-    }
-
-    next();
-  };
-}
-
 export function asyncHandler(
   fn: (req: Request, res: Response, next: NextFunction) => Promise<unknown>,
 ) {