feat: add auth proxy controller for login and token exchange

Adds POST /auth/login and POST /auth/tokens endpoints that proxy
GraphQL mutations to the fortytwo-eap-core platform, letting the
frontend use only the sidecar URL for authentication.

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

src/auth/auth.module.ts

@@ -0,0 +1,7 @@
+import { Module } from '@nestjs/common';
+import { AuthController } from './auth.controller';
+
+@Module({
+    controllers: [AuthController],
+})
+export class AuthModule {}