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/templates/shop/base.html

@@ -136,7 +136,7 @@
                     {# Language Selector #}
                     {% set enabled_langs = vendor.storefront_languages if vendor and vendor.storefront_languages else ['fr', 'de', 'en'] %}
                     {% if enabled_langs|length > 1 %}
-                    <div class="relative" x-data="languageSelector('{{ request.state.language|default("fr") }}', {{ enabled_langs|tojson|safe }})">
+                    <div class="relative" x-data="languageSelector('{{ request.state.language|default('fr') }}', {{ enabled_langs|tojson }})">
                         <button
                             @click="isLangOpen = !isLangOpen"
                             @click.outside="isLangOpen = false"