implement auth login and register with MongoDB

- Add AuthController login/register endpoints with error handling
- Implement AuthService with password validation and user creation
- Add MongoUserRepository with findByEmail and create methods
- Implement password hashing with bcrypt
- Add dotenv for environment variable support
- Add Docker Compose setup for MongoDB + Mongo Express
- Stub AuthMiddleware with fake user for testing
- Update CLAUDE.md with implementation status

apps/server/package.json

@@ -11,6 +11,7 @@
     "@anthropic-ai/sdk": "^0.71.2",
     "@caldav/shared": "*",
     "bcrypt": "^6.0.0",
+    "dotenv": "^16.4.7",
     "express": "^5.2.1",
     "jsonwebtoken": "^9.0.3",
     "mongoose": "^9.1.1"