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_marketplace_service.py

@@ -1,9 +1,9 @@
 # tests/unit/services/test_marketplace_service.py
 """Unit tests for MarketplaceImportJobService."""
+
 import uuid
 
 import pytest
-from unittest.mock import patch
 
 from app.exceptions.base import ValidationException
 from app.exceptions.marketplace_import_job import (
@@ -52,7 +52,9 @@ class TestMarketplaceImportJobService:
 
         assert result.marketplace == "Letzshop"  # Default
 
-    def test_create_import_job_database_error(self, db, test_vendor, test_user, monkeypatch):
+    def test_create_import_job_database_error(
+        self, db, test_vendor, test_user, monkeypatch
+    ):
         """Test import job creation handles database errors."""
         request = MarketplaceImportJobRequest(
             source_url="https://example.com/products.csv",
@@ -119,6 +121,7 @@ class TestMarketplaceImportJobService:
 
     def test_get_import_job_by_id_database_error(self, db, test_user, monkeypatch):
         """Test get import job handles database errors."""
+
         def mock_query(*args):
             raise Exception("Database query failed")
 
@@ -200,7 +203,10 @@ class TestMarketplaceImportJobService:
     ):
         """Test getting import jobs with marketplace filter."""
         jobs = self.service.get_import_jobs(
-            db, test_vendor, test_user, marketplace=test_marketplace_import_job.marketplace
+            db,
+            test_vendor,
+            test_user,
+            marketplace=test_marketplace_import_job.marketplace,
         )
 
         assert len(jobs) >= 1
@@ -254,8 +260,11 @@ class TestMarketplaceImportJobService:
 
         assert len(jobs) == 0
 
-    def test_get_import_jobs_database_error(self, db, test_vendor, test_user, monkeypatch):
+    def test_get_import_jobs_database_error(
+        self, db, test_vendor, test_user, monkeypatch
+    ):
         """Test get import jobs handles database errors."""
+
         def mock_query(*args):
             raise Exception("Database query failed")
 
@@ -270,7 +279,9 @@ class TestMarketplaceImportJobService:
 
     # ==================== convert_to_response_model Tests ====================
 
-    def test_convert_to_response_model(self, db, test_marketplace_import_job, test_vendor):
+    def test_convert_to_response_model(
+        self, db, test_marketplace_import_job, test_vendor
+    ):
         """Test converting database model to response model."""
         from models.database.marketplace_import_job import MarketplaceImportJob as MIJ