feat(ci): lint skills for Codex-safe frontmatter and Claude substitutions

Add scripts/ci/validate-skill-host-compat.js and run it from the Validate
Components job and npm test after validate-skills.js. The check fails on
Claude-only substitutions in bash fences and on Codex copies that use keys
outside name, description, metadata, license, and allowed-tools. CONTRIBUTING
checklist items warn unless --strict-checklist.

Also add /skill-host-compat and skills/skill-host-compat with a Codex copy
that drops origin. Move configure-ecc plugin-root examples into prose so the
live catalog stays green without a skip list.

Co-authored-by: Matt Van Horn <mvanhorn@users.noreply.github.com>

.github/workflows/ci.yml

@@ -211,6 +211,10 @@ jobs:
         run: node scripts/ci/validate-skills.js
         continue-on-error: false
 
+      - name: Validate skill host compatibility
+        run: node scripts/ci/validate-skill-host-compat.js
+        continue-on-error: false
+
       - name: Validate install manifests
         run: node scripts/ci/validate-install-manifests.js
         continue-on-error: false

.github/workflows/reusable-validate.yml

@@ -41,6 +41,9 @@ jobs:
       - name: Validate skills
         run: node scripts/ci/validate-skills.js
 
+      - name: Validate skill host compatibility
+        run: node scripts/ci/validate-skill-host-compat.js
+
       - name: Validate install manifests
         run: node scripts/ci/validate-install-manifests.js