Add portal GitLab pipeline submit

[yoshifuminakamura]

Summary

• add an admin-only Portal submit route for GitLab Pipeline API execution
• keep dry-run and real submit records in execution_requests
• require an explicit confirm_submit checkbox and RESULT_SERVER_GITLAB_TOKEN for real submissions
• document RESULT_SERVER_GITLAB_REPO and RESULT_SERVER_GITLAB_TOKEN usage

Secret handling

• token value is read from the site-local environment only
• token is not stored in SQLite, rendered in the UI, or written to audit details

Validation

• /home/nakamura/fugakunext/venv/bin/python -m pytest result_server/tests/test_execution_profiles.py result_server/tests/test_app_dev_security.py result_server/tests/test_api_routes.py result_server/tests/test_preflight.py
• /home/nakamura/fugakunext/venv/bin/python result_server/tests/run_result_server_tests.py
• python3 -m py_compile result_server/routes/admin.py result_server/utils/gitlab_pipeline.py