🔌 fix: Isolate Code-Server HTTP Agents to Prevent Socket Pool Contamination (#12311)

* 🔧 fix: Isolate HTTP agents for code-server axios requests

Prevents socket hang up after 5s on Node 19+ when code executor has
file attachments. follow-redirects (axios dep) leaks `socket.destroy`
as a timeout listener on TCP sockets; with Node 19+ defaulting to
keepAlive: true, tainted sockets re-enter the global pool and destroy
active node-fetch requests in CodeExecutor after the idle timeout.

Uses dedicated http/https agents with keepAlive: false for all axios
calls targeting CODE_BASEURL in crud.js and process.js.

Closes #12298

* ♻️ refactor: Extract code-server HTTP agents to shared module

- Move duplicated agent construction from crud.js and process.js into
  a shared agents.js module to eliminate DRY violation
- Switch process.js from raw `require('axios')` to `createAxiosInstance()`
  for proxy configuration parity with crud.js
- Fix import ordering in process.js (agent constants no longer split imports)
- Add 120s timeout to uploadCodeEnvFile (was the only code-server call
  without a timeout)

* ✅ test: Add regression tests for code-server socket isolation

- Add crud.spec.js covering getCodeOutputDownloadStream and
  uploadCodeEnvFile (agent options, timeout, URL, error handling)
- Add socket pool isolation tests to process.spec.js asserting
  keepAlive:false agents are forwarded to axios
- Update process.spec.js mocks for createAxiosInstance() migration

* ♻️ refactor: Move code-server agents to packages/api

Relocate agents.js from api/server/services/Files/Code/ to
packages/api/src/utils/code.ts per workspace conventions. Consumers
now import codeServerHttpAgent/codeServerHttpsAgent from @librechat/api.

api/server/services/Files/Code/__tests__/process-traversal.spec.js

@@ -10,11 +10,23 @@ jest.mock('@librechat/agents', () => ({
 
 const mockSanitizeFilename = jest.fn();
 
-jest.mock('@librechat/api', () => ({
-  logAxiosError: jest.fn(),
-  getBasePath: jest.fn(() => ''),
-  sanitizeFilename: mockSanitizeFilename,
-}));
+const mockAxios = jest.fn().mockResolvedValue({
+  data: Buffer.from('file-content'),
+});
+mockAxios.post = jest.fn();
+
+jest.mock('@librechat/api', () => {
+  const http = require('http');
+  const https = require('https');
+  return {
+    logAxiosError: jest.fn(),
+    getBasePath: jest.fn(() => ''),
+    sanitizeFilename: mockSanitizeFilename,
+    createAxiosInstance: jest.fn(() => mockAxios),
+    codeServerHttpAgent: new http.Agent({ keepAlive: false }),
+    codeServerHttpsAgent: new https.Agent({ keepAlive: false }),
+  };
+});
 
 jest.mock('librechat-data-provider', () => ({
   ...jest.requireActual('librechat-data-provider'),
@@ -53,12 +65,6 @@ jest.mock('~/server/utils', () => ({
   determineFileType: jest.fn().mockResolvedValue({ mime: 'text/csv' }),
 }));
 
-jest.mock('axios', () =>
-  jest.fn().mockResolvedValue({
-    data: Buffer.from('file-content'),
-  }),
-);
-
 const { createFile } = require('~/models');
 const { processCodeOutput } = require('../process');