fix: Resolve frontend API connection issues in Docker

- Add setupProxy.js to proxy API calls to backend container
- Install http-proxy-middleware for development proxy support
- Update docker-compose.dev.yml to use backend service name
- Add HOST=0.0.0.0 to allow external connections to dev server
- Add empty favicon.ico to prevent 500 errors
- Update proxy configuration to use port 7510

This fixes the ERR_CONNECTION_REFUSED errors when the frontend
tries to connect to the backend API in Docker environment.

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

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

frontend/package-lock.json

@@ -40,6 +40,7 @@
         "eslint-plugin-prettier": "^5.1.2",
         "eslint-plugin-react": "^7.33.2",
         "eslint-plugin-react-hooks": "^4.6.0",
+        "http-proxy-middleware": "^2.0.9",
         "prettier": "^3.1.1"
       }
     },