release: publish v0.5.1 onboarding and metadata

[Mresyzz]

What changed

• Bump the package and Action to v0.5.1 so the corrected public documentation reaches PyPI and the Marketplace listing.
• Update the Action and PyPI descriptions to state the container matrix and runtime compatibility use case.
• Point generated workflows and maintained examples at v0.5.1.
• Record the patch release in CHANGELOG.md.

Validation

• python -m pytest -q — 97 passed, 4 skipped
• python -m build — built opsscript_gate-0.5.1 wheel and sdist
• git diff --check — passed

Merging this PR is the intentional v0.5.1 release trigger.