🔌 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/crud.js

@@ -1,6 +1,11 @@
 const FormData = require('form-data');
 const { getCodeBaseURL } = require('@librechat/agents');
-const { createAxiosInstance, logAxiosError } = require('@librechat/api');
+const {
+  logAxiosError,
+  createAxiosInstance,
+  codeServerHttpAgent,
+  codeServerHttpsAgent,
+} = require('@librechat/api');
 
 const axios = createAxiosInstance();
 
@@ -25,6 +30,8 @@ async function getCodeOutputDownloadStream(fileIdentifier, apiKey) {
         'User-Agent': 'LibreChat/1.0',
         'X-API-Key': apiKey,
       },
+      httpAgent: codeServerHttpAgent,
+      httpsAgent: codeServerHttpsAgent,
       timeout: 15000,
     };
 
@@ -69,6 +76,9 @@ async function uploadCodeEnvFile({ req, stream, filename, apiKey, entity_id = ''
         'User-Id': req.user.id,
         'X-API-Key': apiKey,
       },
+      httpAgent: codeServerHttpAgent,
+      httpsAgent: codeServerHttpsAgent,
+      timeout: 120000,
       maxContentLength: MAX_FILE_SIZE,
       maxBodyLength: MAX_FILE_SIZE,
     };