feat(proxy): add outbound HTTP proxy support for OAuth + provider requests

- Patch Node fetch via undici ProxyAgent when HTTP_PROXY/HTTPS_PROXY/ALL_PROXY is set
- Ensure proxy patch is loaded for both chat pipeline and OAuth token exchange
- Add Dashboard Settings → Network to edit outbound proxy and apply immediately
- Persist outbound proxy settings in local db and initialize on server startup
- Move proxy helpers to src/lib/network/ for better structure
- Rename src/proxy.js → src/dashboardGuard.js to avoid naming confusion
- Re-apply proxy env after DB import
- Fix: close old dispatcher on proxy URL change to prevent connection pool leak
- Fix: idempotency guard to avoid patching globalThis.fetch multiple times

Made-with: Cursor

package.json

@@ -19,7 +19,6 @@
     "express": "^5.2.1",
     "fs": "^0.0.1-security",
     "http-proxy-middleware": "^3.0.5",
-    "https-proxy-agent": "^7.0.6",
     "jose": "^6.1.3",
     "lowdb": "^7.0.1",
     "monaco-editor": "^0.55.1",