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>

app/api/v1/vendor/letzshop.py

@@ -323,9 +323,7 @@ def get_order(
     order_service = get_order_service(db)
 
     try:
-        order = order_service.get_order_or_raise(
-            current_user.token_vendor_id, order_id
-        )
+        order = order_service.get_order_or_raise(current_user.token_vendor_id, order_id)
     except OrderNotFoundError:
         raise ResourceNotFoundException("LetzshopOrder", str(order_id))
 
@@ -396,7 +394,9 @@ def import_orders(
                         orders_imported += 1
 
                 except Exception as e:
-                    errors.append(f"Error processing shipment {shipment.get('id')}: {e}")
+                    errors.append(
+                        f"Error processing shipment {shipment.get('id')}: {e}"
+                    )
 
             db.commit()
             creds_service.update_sync_status(
@@ -475,9 +475,7 @@ def confirm_order(
             return FulfillmentOperationResponse(
                 success=True,
                 message=f"Confirmed {len(inventory_unit_ids)} inventory units",
-                confirmed_units=[
-                    u.get("id") for u in result.get("inventoryUnits", [])
-                ],
+                confirmed_units=[u.get("id") for u in result.get("inventoryUnits", [])],
             )
 
     except LetzshopClientError as e:
@@ -699,7 +697,9 @@ def list_fulfillment_queue(
 
 @router.get("/export")
 def export_products_letzshop(
-    language: str = Query("en", description="Language for title/description (en, fr, de)"),
+    language: str = Query(
+        "en", description="Language for title/description (en, fr, de)"
+    ),
     include_inactive: bool = Query(False, description="Include inactive products"),
     current_user: User = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),