fix: resolve homepage sections editor and rendering issues

- Fix sections editor not showing by converting isHomepage getter to property
- Add Alpine Collapse plugin for accordion animations
- Fix Quill editor content not syncing after page load
- Add platform dropdown to content page edit form
- Create shared templates config (app/templates_config.py) with i18n globals
  to make _() translation function available in Jinja2 macros
- Fix pricing template field names (monthly_price → price_monthly)
- Fix translation key (pricing.save_20 → pricing.save_months)
- Add tiers context to CMS homepage route for pricing section
- Fix architecture validation issues (language defaults, inline SVGs → $icon)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/templates/platform/homepage-default.html

@@ -22,7 +22,7 @@
 
 {% block content %}
 {# Set up language context #}
-{% set lang = request.state.language or (platform.default_language if platform else 'fr') %}
+{% set lang = request.state.language|default("fr") or (platform.default_language if platform else 'fr') %}
 {% set default_lang = platform.default_language if platform else 'fr' %}
 
 {# ═══════════════════════════════════════════════════════════════════════════ #}