Add PR check requiring plugin version bump on plugin-directory changes

[jodavis-claude]

Summary

• Adds a required PR check: any PR touching plugins/<name>/ must raise that plugin's version in plugin.json above the version on main, or the check fails.
• Generic over plugins/*/ (works if more plugins are added later), evaluates every touched plugin independently, and reports all violations in one run.
• No automated version-bump tooling (changesets/release-please) — considered and explicitly descoped since both assume a deferred-bump model that conflicts with the manual bump-in-place approach here.

Changes

• scripts/check_plugin_versions.py — stdlib-only Python checker (no third-party deps).
• scripts/test_check_plugin_versions.py — 25 pytest unit tests covering new/deleted plugins, unchanged/lowered versions, invalid semver, multi-plugin PRs.
• .github/workflows/plugin-version-check.yml — triggers on PRs targeting main only (not intermediate stacked-PR branches); a gate job skips the rest when no plugins/** files changed; check-versions runs the checker; test-script runs the unit tests unconditionally.

Test plan

• python3 -m pytest scripts/test_check_plugin_versions.py -v — 25/25 passing
• Manually verified in a disposable worktree: fails when a plugin file changes without a version bump, passes once bumped, no-ops when no plugin dir is touched
• Confirm the new workflow runs correctly on this PR (touches .github/workflows/ and scripts/, not plugins/, so check-versions should be gated off and only test-script should run)

🤖 Generated with Claude Code

https://claude.ai/code/session_0169tvYH3dirw6Fc1EPRQ3S8

[github-actions]

build-and-test: Python test results

Status: ✅ Passed

Test log