⚖️ refactor: Split Config Route into Unauthenticated and Authenticated Paths (#12490)

* refactor: split /api/config into unauthenticated and authenticated response paths

- Replace preAuthTenantMiddleware with optionalJwtAuth on the /api/config
  route so the handler can detect whether the request is authenticated
- When unauthenticated: call getAppConfig({ baseOnly: true }) for zero DB
  queries, return only login-relevant fields (social logins, turnstile,
  privacy policy / terms of service from interface config)
- When authenticated: call getAppConfig({ role, userId, tenantId }) to
  resolve per-user DB overrides (USER + ROLE + GROUP + PUBLIC principals),
  return full payload including modelSpecs, balance, webSearch, etc.
- Extract buildSharedPayload() and addWebSearchConfig() helpers to avoid
  duplication between the two code paths
- Fixes per-user balance overrides not appearing in the frontend because
  userId was never passed to getAppConfig (follow-up to #12474)

* test: rewrite config route tests for unauthenticated vs authenticated paths

- Replace the previously-skipped supertest tests with proper mocked tests
- Cover unauthenticated path: baseOnly config call, minimal payload,
  interface subset (privacyPolicy/termsOfService only), exclusion of
  authenticated-only fields
- Cover authenticated path: getAppConfig called with userId, full payload
  including modelSpecs/balance/webSearch, per-user balance override merging

* fix: address review findings — restore multi-tenant support, improve tests

- Chain preAuthTenantMiddleware back before optionalJwtAuth on /api/config
  so unauthenticated requests in multi-tenant deployments still get
  tenant-scoped config via X-Tenant-Id header (Finding #1)
- Use getAppConfig({ tenantId }) instead of getAppConfig({ baseOnly: true })
  when a tenant context is present; fall back to baseOnly for single-tenant
- Fix @type annotation: unauthenticated payload is Partial<TStartupConfig>
- Refactor addWebSearchConfig into pure buildWebSearchConfig that returns a
  value instead of mutating the payload argument
- Hoist isBirthday() to module level
- Remove inline narration comments
- Assert tenantId propagation in tests, including getTenantId fallback and
  user.tenantId preference
- Add error-path tests for both unauthenticated and authenticated branches
- Expand afterEach env var cleanup for proper test isolation

* test: fix mock isolation and add tenant-scoped response test

- Replace jest.clearAllMocks() with jest.resetAllMocks() so
  mockReturnValue implementations don't leak between tests
- Add test verifying tenant-scoped socialLogins and turnstile are
  correctly mapped in the unauthenticated response

* fix: add optionalJwtAuth to /api/config in experimental.js

Without this middleware, req.user is never populated in the experimental
cluster entrypoint, so authenticated users always receive the minimal
unauthenticated config payload.

api/server/experimental.js

@@ -19,6 +19,7 @@ const {
   performStartupChecks,
   handleJsonParseError,
   initializeFileStorage,
+  preAuthTenantMiddleware,
 } = require('@librechat/api');
 const { connectDb, indexSync } = require('~/db');
 const initializeOAuthReconnectManager = require('./services/initializeOAuthReconnectManager');
@@ -31,6 +32,7 @@ const initializeMCPs = require('./services/initializeMCPs');
 const configureSocialLogins = require('./socialLogins');
 const { getAppConfig } = require('./services/Config');
 const staticCache = require('./utils/staticCache');
+const optionalJwtAuth = require('./middleware/optionalJwtAuth');
 const noIndex = require('./middleware/noIndex');
 const routes = require('./routes');
 
@@ -312,7 +314,7 @@ if (cluster.isMaster) {
     app.use('/api/endpoints', routes.endpoints);
     app.use('/api/balance', routes.balance);
     app.use('/api/models', routes.models);
-    app.use('/api/config', routes.config);
+    app.use('/api/config', preAuthTenantMiddleware, optionalJwtAuth, routes.config);
     app.use('/api/assistants', routes.assistants);
     app.use('/api/files', await routes.files.initialize());
     app.use('/images/', createValidateImageRequest(appConfig.secureImageLinks), routes.staticRoute);