Add all-done aggregator job to prevent cancelled jobs appearing as failures

Cancelled jobs from concurrent workflow runs show as red failures in PR
checks. The all-done job depends on lint and docs (which aggregate all
build jobs), runs with if: always(), and only fails on real failures —
not cancellations or skips. Configure branch protection to require
All Done as the single required check.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: leogdion

.github/workflows/SyntaxKit.yml

@@ -344,3 +344,17 @@ jobs:
       - uses: actions/checkout@v6
       - name: Validate Documentation
         run: ./Scripts/validate-docs.sh
+
+  all-done:
+    name: All Done
+    if: always()
+    needs: [lint, docs]
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check for failures
+        run: |
+          if [[ "${{ contains(needs.*.result, 'failure') }}" == "true" ]]; then
+            echo "One or more required jobs failed."
+            exit 1
+          fi
+          echo "All required checks passed, were skipped, or were cancelled."