ci: add skills-ref lint step for SKILL.md validation

.github/workflows/ci.yml

@@ -36,6 +36,7 @@ jobs:
     outputs:
       rust: ${{ steps.filter.outputs.rust }}
       nix: ${{ steps.filter.outputs.nix }}
+      skills: ${{ steps.filter.outputs.skills }}
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
       - uses: dorny/paths-filter@de90cc6fb38fc0963ad72b210f1f284cd68cea36 # v3
@@ -52,6 +53,8 @@ jobs:
             nix:
               - 'flake.nix'
               - 'flake.lock'
+            skills:
+              - 'skills/**'
 
   test:
     name: Test
@@ -190,6 +193,27 @@ jobs:
             echo "::warning::Skills are out of date — the hourly auto-sync PR will fix this automatically."
           fi
 
+  lint-skills:
+    name: Lint Skills
+    needs: changes
+    if: needs.changes.outputs.skills == 'true' || github.event_name == 'push'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+
+      - name: Validate skills
+        run: |
+          failed=0
+          for skill_dir in skills/*/; do
+            if ! uvx --from skills-ref@0.1.1 agentskills validate "$skill_dir"; then
+              failed=1
+            fi
+          done
+          if [ "$failed" -ne 0 ]; then
+            echo "::error::One or more skills failed validation."
+            exit 1
+          fi
+
   build-linux:
     name: Build (Linux x86_64)
     needs: changes