feat: Complete backend API setup with registration endpoint

- Added user registration endpoint (/api/v1/auth/register)
- Created MongoDB database connection module
- Fixed user models to match frontend signup form
- Exposed backend port 8000 for development
- Configured Vite proxy for API requests
- Successfully tested user registration flow

Backend is now fully functional with:
- MongoDB connection
- User registration with password hashing
- JWT token generation
- Proper error handling

🤖 Generated with [Claude Code](https://claude.ai/code)

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

oauth/backend/app/db/mongodb.py

@@ -0,0 +1,20 @@
+import os
+from motor.motor_asyncio import AsyncIOMotorClient
+from typing import Optional
+
+mongodb_client: Optional[AsyncIOMotorClient] = None
+database = None
+
+async def connect_to_mongo():
+    global mongodb_client, database
+    mongodb_url = os.getenv("MONGODB_URL", "mongodb://localhost:27017")
+    mongodb_client = AsyncIOMotorClient(mongodb_url)
+    database = mongodb_client.oauth_db
+
+async def close_mongo_connection():
+    global mongodb_client
+    if mongodb_client:
+        mongodb_client.close()
+
+async def get_database():
+    return database