Fix CI workflow to use Zensical build command

Update GitHub workflow and justfile to use 'zensical build --strict'
instead of 'mkdocs build --strict', aligning with the v0.2.1 migration
to Zensical. The --strict flag is added for future compatibility when
Zensical implements strict validation mode.

Author: SmileyChris

.github/workflows/tests.yml

@@ -74,7 +74,7 @@ jobs:
         run: uv run mypy graphql_sqlcommenter
 
       - name: Check documentation
-        run: uv run --group docs mkdocs build --strict
+        run: uv run --group docs zensical build --strict
 
       - name: Run security scan
         run: uv run bandit -r graphql_sqlcommenter -x tests

justfile

@@ -114,7 +114,7 @@ check:
     @echo "✓ Type checking OK"
     @echo ""
     @echo "→ Validating documentation..."
-    uv run --group docs zensical build
+    uv run --group docs zensical build --strict
     @echo "✓ Documentation OK"
     @echo ""
     @echo "→ Running tests..."