Test GitLab MCP server modular architecture with real GitLab resources

## Summary

After refactoring the GitLab MCP server from monolithic to modular architecture, we need comprehensive testing to ensure all 53 tools work correctly with real GitLab resources.

## Test Scope

**Tools to test (53 total):**
- Pipeline Operations (7 tools): `gitlab_list_pipelines`, `gitlab_get_pipeline`, `gitlab_get_pipeline_jobs`, `gitlab_get_job_log`, `gitlab_get_failed_jobs`, `gitlab_retry_job`, `gitlab_cancel_pipeline`
- Project Management (10 tools): `gitlab_list_projects`, `gitlab_get_project`, `gitlab_create_project`, `gitlab_list_branches`, `gitlab_get_branch`, `gitlab_create_branch`, `gitlab_delete_branch`, `gitlab_list_tags`, `gitlab_get_tag`, `gitlab_create_tag`, `gitlab_delete_tag`
- Basic Operations (5 tools): `gitlab_list_issues`, `gitlab_get_issue`, `gitlab_list_merge_requests`, `gitlab_get_merge_request`, `gitlab_get_file`
- User/Group Management (7 tools): `gitlab_get_user`, `gitlab_list_users`, `gitlab_get_current_user`, `gitlab_list_groups`, `gitlab_get_group`, `gitlab_list_group_members`, `gitlab_list_project_members`
- Issue Management (10 tools): `gitlab_create_issue`, `gitlab_update_issue`, `gitlab_close_issue`, `gitlab_reopen_issue`, `gitlab_list_issue_comments`, `gitlab_create_issue_comment`, `gitlab_list_project_labels`, `gitlab_create_project_label`, `gitlab_list_project_milestones`, `gitlab_create_project_milestone`
- Merge Request Operations (11 tools): `gitlab_create_merge_request`, `gitlab_update_merge_request`, `gitlab_merge_merge_request`, `gitlab_close_merge_request`, `gitlab_reopen_merge_request`, `gitlab_list_mr_comments`, `gitlab_create_mr_comment`, `gitlab_get_mr_diff`, `gitlab_get_mr_changes`, `gitlab_approve_merge_request`, `gitlab_unapprove_merge_request`

## Testing Approach

**Real Resource Testing** (not just unit tests):
1. Create test GitLab project
2. Test each tool category with real GitLab API calls
3. Create/modify/delete actual resources (projects, issues, MRs, etc.)
4. Verify tool responses and functionality
5. Clean up test resources

## Test Plan

1. **Setup**: Create dedicated test GitLab project
2. **Pipeline Testing**: Test CI/CD pipeline operations
3. **Project Testing**: Test project, branch, and tag operations
4. **Issue Testing**: Test full issue lifecycle (create → update → comment → close)
5. **MR Testing**: Test full merge request lifecycle (create → update → comment → approve → merge)
6. **User/Group Testing**: Test user and group management operations
7. **Cleanup**: Remove all test resources

## Acceptance Criteria

- [ ] All 53 tools execute without errors
- [ ] Tool responses match expected schemas
- [ ] Real GitLab resources are created/modified/deleted as expected
- [ ] All test resources are properly cleaned up
- [ ] Modular architecture maintains exact same functionality as monolithic version

## Related

- Refactoring PR: [Link to modular architecture PR]
- GitLab MCP Server: `mcp/servers/gitlab-mcp-server/`

Priority: High - Required before considering modular refactoring complete

Start in mcp/servers/gitlab-mcp-server/ and review the modular architecture context before defining the real-resource test setup. Exercise the 53 listed tools across pipeline, project, issue, merge request, and user/group operations, then verify response schemas, resource changes, and cleanup against the acceptance criteria.

Written by the indexing model from the issue text.