feat(web): add GitLab issues/MRs server module

Add a server-side GitLab integration mirroring the GitHub module:
- auth.js: PAT auth storage with multi-account support and configurable
  base URL (gitlab.com default, self-hosted instances supported)
- client.js: raw-fetch GitLab REST v4 client with per-request timeout,
  ETag conditional-GET cache, own rate-limit cooldown, pagination, and
  single-follow redirect handling
- repo.js: GitLab remote URL parser + directory resolution
- routes.js: read-only /api/gitlab/* routes (auth, issues, MRs, branches)
- index.js + DOCUMENTATION.md + unit tests for auth, client, repo, routes
- Wire registerGitLabRoutes into feature-routes-runtime

packages/web/server/lib/gitlab/index.js

@@ -0,0 +1,22 @@
+export {
+  getGitLabAuth,
+  getGitLabAuthAccounts,
+  setGitLabAuth,
+  activateGitLabAuth,
+  clearGitLabAuth,
+  normalizeBaseUrl,
+  GITLAB_AUTH_FILE,
+  DEFAULT_GITLAB_BASE_URL,
+} from './auth.js';
+
+export {
+  createGitLabClient,
+  getGitLabClientOrNull,
+  isGitLabRateLimited,
+  noteGitLabRateLimit,
+} from './client.js';
+
+export {
+  parseGitLabRemoteUrl,
+  resolveGitLabRepoFromDirectory,
+} from './repo.js';