fix: quote four skill descriptions that break YAML frontmatter, add a CI check

[ziyiunity]

Fixes #44.

What

Four skills have an unquoted description: whose text contains ": " (colon followed by a space). A strict YAML parser reads that as a nested mapping and fails with mapping values are not allowed here, so agents that parse the frontmatter drop the skill silently. claude plugin list still reports the plugin as enabled; the only symptom is a shorter skill list.

Affected: ui, ui-imgui, physics-3d-collision, tilemap-ruletile-createfromsegment. ui is the routing entry point for the whole UI family, so its absence matters most.

Fix

Rewrite the four descriptions as folded block scalars (>-), the form optimize-text-mesh-pro and setup-multiplayer-services already use. The text is unchanged: the parsed value of each description is byte-identical to the old plain scalar, verified by parsing both. Only the frontmatter lines change; skill bodies are untouched.

Add scripts/check-skill-frontmatter.mjs and a Validate skills workflow that parses every skills/*/SKILL.md frontmatter with js-yaml (the parser Claude Code ships) and requires a non-empty name matching the folder and a non-empty description. Against main it reports exactly these four files; after this change all 31 pass.

Also updates the codex plugin list sample in the README from 0.1.0-beta to the current 0.1.6-beta.

Verify

npm install --no-save js-yaml@4
node scripts/check-skill-frontmatter.mjs skills