fix: verify powermem-mcp PyPI release publishing

[knqiufan]

Summary

• Add a PyPI release verification script that checks both powermem and powermem-mcp publish the requested version with wheel and sdist artifacts.
• Run the verification after the powermem-mcp publish job so missing wrapper releases fail the publish workflow instead of passing silently.
• Update release docs to describe the two PyPI projects, Trusted Publisher setup, and the backfill flow for missing package versions.

Test Plan

• python -m pytest tests/unit/test_check_pypi_release.py -v
• python -m pytest tests/unit/test_release_binary_ci.py::test_pypi_publish_workflow_verifies_both_python_packages -v
• python scripts/check_package_versions.py
• git diff --cached --check

Notes

• The powermem-mcp PyPI project still needs a Trusted Publisher entry for oceanbase/powermem and publish.yml before the failed release can be backfilled.

Closes #1117

[wayyoungboy]

Reviewed the publish workflow and the new PyPI visibility checker. The verification job waits for the powermem-mcp publish job, checks both powermem and powermem-mcp, and the script correctly validates the requested release version plus wheel/sdist presence with retries.

Targeted verification passed locally: tests/unit/test_check_pypi_release.py and tests/unit/test_release_binary_ci.py (24 tests). No blocker from my side.