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/unit/services/test_letzshop_service.py

@@ -8,26 +8,22 @@ Tests cover:
 - GraphQL client (mocked)
 """
 
-import pytest
 from unittest.mock import MagicMock, patch
 
+import pytest
+
 from app.services.letzshop import (
-    LetzshopClient,
-    LetzshopClientError,
-    LetzshopAuthError,
-    LetzshopAPIError,
-    LetzshopCredentialsService,
     CredentialsNotFoundError,
+    LetzshopAPIError,
+    LetzshopClient,
+    LetzshopCredentialsService,
 )
 from app.utils.encryption import (
-    EncryptionService,
     EncryptionError,
-    encrypt_value,
-    decrypt_value,
+    EncryptionService,
     mask_api_key,
 )
 
-
 # ============================================================================
 # Encryption Tests
 # ============================================================================
@@ -339,9 +335,7 @@ class TestLetzshopClient:
         """Test successful connection test."""
         mock_response = MagicMock()
         mock_response.status_code = 200
-        mock_response.json.return_value = {
-            "data": {"__typename": "Query"}
-        }
+        mock_response.json.return_value = {"data": {"__typename": "Query"}}
         mock_post.return_value = mock_response
 
         client = LetzshopClient(api_key="test-key")
@@ -398,7 +392,7 @@ class TestLetzshopClient:
                     "inventoryUnits": [
                         {"id": "unit_1", "state": "confirmed"},
                     ],
-                    "errors": []
+                    "errors": [],
                 }
             }
         }
@@ -420,12 +414,9 @@ class TestLetzshopClient:
                 "setShipmentTracking": {
                     "shipment": {
                         "id": "ship_1",
-                        "tracking": {
-                            "code": "1Z999AA1",
-                            "provider": "ups"
-                        }
+                        "tracking": {"code": "1Z999AA1", "provider": "ups"},
                     },
-                    "errors": []
+                    "errors": [],
                 }
             }
         }
@@ -446,9 +437,7 @@ class TestLetzshopClient:
         mock_response = MagicMock()
         mock_response.status_code = 200
         mock_response.json.return_value = {
-            "errors": [
-                {"message": "Invalid shipment ID"}
-            ]
+            "errors": [{"message": "Invalid shipment ID"}]
         }
         mock_post.return_value = mock_response