fix: Resolve registration API 500 error and proxy configuration

- Fixed undefined variable 'db' in register endpoint (renamed to 'database')
- Updated Vite proxy configuration to use Docker container names
- Fixed proxy target from localhost to backend container
- Added host: true to Vite server config for Docker compatibility
- Registration endpoint now works correctly through frontend proxy

All registration functionality is now fully operational:
- Frontend form validation
- API proxy routing
- Backend user creation
- JWT token generation
- MongoDB data persistence

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

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

oauth/frontend/vite.config.ts

@@ -5,9 +5,10 @@ import react from '@vitejs/plugin-react'
 export default defineConfig({
   plugins: [react()],
   server: {
+    host: true,
     proxy: {
       '/api': {
-        target: 'http://localhost:8000',
+        target: 'http://backend:8000',
         changeOrigin: true,
         secure: false,
       }