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/integration/middleware/test_vendor_context_flow.py

@@ -441,7 +441,9 @@ class TestVendorContextFlow:
             mock_settings.platform_domain = "platform.com"
             response = client.get(
                 "/test-inactive-vendor-detection",
-                headers={"host": f"{middleware_inactive_vendor.subdomain}.platform.com"},
+                headers={
+                    "host": f"{middleware_inactive_vendor.subdomain}.platform.com"
+                },
             )
 
         assert response.status_code == 200