chore: prepare 0.9.0 release

[rlippmann]

What changed

• Set the package version to 0.9.0 and update the lockfile.
• Add release-tag verification and built-artifact smoke checks to the PyPI workflow.
• Update README links for the release repository layout.

Why

Prepare the Python package and release workflow for the 0.9.0 release.

Checklist

• pre-commit run (uv run pre-commit run --all-files)
• tests pass (uv run pytest)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (fa6075c) to head (f56948f).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #274   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          784       784           
=========================================
  Hits           784       784           

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