fix: correct tojson|safe usage in templates and update validator

- Remove |safe from |tojson in HTML attributes (x-data) - quotes must
  become " for browsers to parse correctly
- Update LANG-002 and LANG-003 architecture rules to document correct
  |tojson usage patterns:
  - HTML attributes: |tojson (no |safe)
  - Script blocks: |tojson|safe
- Fix validator to warn when |tojson|safe is used in x-data (breaks
  HTML attribute parsing)
- Improve code quality across services, APIs, and tests

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/system/test_error_handling.py

@@ -88,9 +88,7 @@ class TestErrorHandling:
 
     def test_marketplace_product_not_found(self, client, admin_headers):
         """Test accessing non-existent marketplace product"""
-        response = client.get(
-            "/api/v1/admin/products/999999", headers=admin_headers
-        )
+        response = client.get("/api/v1/admin/products/999999", headers=admin_headers)
 
         assert response.status_code == 404
         data = response.json()