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

src/app/api/settings/proxy-test/route.js

@@ -0,0 +1,23 @@
+import { NextResponse } from "next/server";
+import { testProxyUrl } from "@/lib/network/proxyTest";
+
+export async function POST(request) {
+  try {
+    const body = await request.json();
+    const result = await testProxyUrl({
+      proxyUrl: body?.proxyUrl,
+      testUrl: body?.testUrl,
+      timeoutMs: body?.timeoutMs,
+    });
+
+    if (result?.ok) {
+      return NextResponse.json(result);
+    }
+
+    const status = typeof result?.status === "number" ? result.status : 500;
+    return NextResponse.json({ ok: false, error: result?.error || "Proxy test failed" }, { status });
+  } catch (err) {
+    const message = err?.name === "AbortError" ? "Proxy test timed out" : (err?.message || String(err));
+    return NextResponse.json({ ok: false, error: message }, { status: 500 });
+  }
+}