Harden documentation deployment verification - #33

What changed

• move public documentation identity verification into a tested CI script
• send an explicit release-verifier user agent accepted by ml4trading.io
• use a distinct cache-busting query for each retry
• report the last observed payload or request error on failure

Root cause

The stable release deployed both documentation trees successfully, but Python's default urllib
user agent receives HTTP 403 from ml4trading.io. The inline workflow swallowed that response and
timed out without diagnostics.

Impact

Stable releases can verify the deployed revision before publishing the already-qualified candidate
to PyPI.

Validation

• uv run pytest -q (408 passed)
• uv run ruff check and uv run ruff format --check on changed Python files
• uv run ty check scripts/ci/verify_docs_deployment.py
• end-to-end verifier request against the deployed 0.1.0 stable and versioned markers