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/models/database/test_product.py

@@ -1,5 +1,6 @@
 # tests/unit/models/database/test_product.py
 """Unit tests for Product (vendor catalog) database model."""
+
 import pytest
 from sqlalchemy.exc import IntegrityError
 
@@ -35,10 +36,9 @@ class TestProductModel:
         assert product.is_featured is True
         assert product.vendor.vendor_code == test_vendor.vendor_code
         # Use get_title() method instead of .title attribute
-        assert (
-            product.marketplace_product.get_title("en")
-            == test_marketplace_product.get_title("en")
-        )
+        assert product.marketplace_product.get_title(
+            "en"
+        ) == test_marketplace_product.get_title("en")
 
     def test_product_unique_per_vendor(self, db, test_vendor, test_marketplace_product):
         """Test that same marketplace product can't be added twice to vendor catalog."""
@@ -75,7 +75,9 @@ class TestProductModel:
         assert product.min_quantity == 1  # Default
         assert product.display_order == 0  # Default
 
-    def test_product_vendor_override_fields(self, db, test_vendor, test_marketplace_product):
+    def test_product_vendor_override_fields(
+        self, db, test_vendor, test_marketplace_product
+    ):
         """Test Product model vendor-specific override fields."""
         product = Product(
             vendor_id=test_vendor.id,
@@ -97,7 +99,9 @@ class TestProductModel:
         assert product.currency == "USD"
         assert product.availability == "limited"
 
-    def test_product_inventory_settings(self, db, test_vendor, test_marketplace_product):
+    def test_product_inventory_settings(
+        self, db, test_vendor, test_marketplace_product
+    ):
         """Test Product model inventory settings."""
         product = Product(
             vendor_id=test_vendor.id,
@@ -126,7 +130,9 @@ class TestProductModel:
         assert product.marketplace_product is not None
         assert product.inventory_entries == []  # No inventory yet
 
-    def test_product_effective_properties(self, db, test_vendor, test_marketplace_product):
+    def test_product_effective_properties(
+        self, db, test_vendor, test_marketplace_product
+    ):
         """Test Product effective properties with override pattern."""
         # First, set some values on the marketplace product
         test_marketplace_product.price_numeric = 100.00