Add CI workflow to validate agent file format

Adds a lint script and GitHub Actions workflow that checks agent
markdown files for required YAML frontmatter fields (name, description,
color) and recommends standard sections. Only changed files in PRs
are validated to avoid blocking on pre-existing issues.

.github/workflows/lint-agents.yml

@@ -0,0 +1,44 @@
+name: Lint Agent Files
+
+on:
+  pull_request:
+    paths:
+      - 'design/**'
+      - 'engineering/**'
+      - 'marketing/**'
+      - 'product/**'
+      - 'project-management/**'
+      - 'testing/**'
+      - 'support/**'
+      - 'spatial-computing/**'
+      - 'specialized/**'
+
+jobs:
+  lint:
+    name: Validate agent frontmatter and structure
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Get changed agent files
+        id: changed
+        run: |
+          FILES=$(git diff --name-only --diff-filter=ACMR origin/${{ github.base_ref }}...HEAD -- \
+            'design/*.md' 'engineering/*.md' 'marketing/*.md' 'product/*.md' \
+            'project-management/*.md' 'testing/*.md' 'support/*.md' \
+            'spatial-computing/*.md' 'specialized/*.md')
+          echo "files=$FILES" >> "$GITHUB_OUTPUT"
+          if [ -z "$FILES" ]; then
+            echo "No agent files changed."
+          else
+            echo "Changed files:"
+            echo "$FILES"
+          fi
+
+      - name: Run agent linter
+        if: steps.changed.outputs.files != ''
+        run: |
+          chmod +x scripts/lint-agents.sh
+          ./scripts/lint-agents.sh ${{ steps.changed.outputs.files }}