Add a central documentation pilot for PyPTO

[lyfne123]

Summary

Build the homepage and a successful upstream PyPTO Docs snapshot as one artifact, using the website checkout's shared theme. This pilots central deployment before adding the other four projects and full-site search. Automatic builds and Pages publishing remain disabled until explicitly configured; current production routes are unchanged.

Changes

• Accept CI notifications or manual requests, verify the upstream main Docs run through GitHub, and freeze its source SHA in a build manifest.
• Run the existing PyPTO documentation checks and strict bilingual build, then package only the homepage, its assets, /pypto/, and provenance.
• Guard publication against superseded source/workflow revisions and unchanged inputs; provide scheduled notification recovery and document the App and Pages handoff settings.

Verification

• python -m pytest tests/test_docs_site.py -q: 35 passed.
• python -m pytest tests/test_browser_theme.py -q against the fresh PyPTO build: 24 passed.
• ruff check scripts/docs_site.py tests/test_docs_site.py and ruff format --check scripts/docs_site.py tests/test_docs_site.py: passed.
• actionlint -color .github/workflows/docs-site.yml: passed.
• PyPTO navigation, EN/ZH parity, symbol coverage, op docstring checks, python -m pip check, and python -m mkdocs build --strict: passed.
• python tests/docs_theme_compat.py check --site .docs-build/pypto/site --project pypto --page api/tile/index.html: four rendered pages passed.
• Receiver resolution and the read-only publication guard accepted real GitHub run metadata before committing. No workflow dispatch or Pages deployment was performed: both default-branch workflows and the GitHub App configuration are required for that live test.
• Hosted GitHub Actions: the central pilot build and all five existing theme compatibility jobs passed. The uploaded docs-site-pilot artifact was downloaded and checked: homepage, EN/ZH PyPTO pages, API pages, search data, and source manifest are present; four rendered-page checks passed. Pages deployment was skipped as intended.