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/services/stats_service.py

@@ -160,7 +160,9 @@ class StatsService:
                 # Inventory stats
                 "total_inventory_quantity": int(total_inventory),
                 "reserved_inventory_quantity": int(reserved_inventory),
-                "available_inventory_quantity": int(total_inventory - reserved_inventory),
+                "available_inventory_quantity": int(
+                    total_inventory - reserved_inventory
+                ),
                 "inventory_locations_count": inventory_locations,
             }