feat(i18n): complete post-launch i18n phases 5-8

- Phase 5: Translate homepage-modern.html (~90 new locale keys, all
  hardcoded strings replaced with _() calls for dashboard mock,
  features, pricing tiers, testimonial sections)
- Phase 6: Translate homepage-minimal.html (17 new locale keys for
  fallback content, features, and CTA sections)
- Phase 7: Add multi-language page.title/content support with
  title_translations and content_translations JSON columns, Alembic
  migration cms_002, translated title/content resolution in templates,
  and seed script updates with tt() helper
- Phase 8: Complete lb.json audit — fill 6 missing keys (messages,
  confirmations), also backfill same keys in fr.json and de.json

All 4 locale files now have 340 keys with full parity.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/templates/platform/base.html

@@ -75,7 +75,7 @@
                         {% for page in header_pages %}
                         <a href="/{{ page.slug }}"
                            class="text-gray-700 dark:text-gray-300 hover:text-indigo-600 dark:hover:text-indigo-400 font-medium transition-colors">
-                            {{ page.title }}
+                            {{ page.get_translated_title(current_language|default('fr')) }}
                         </a>
                         {% endfor %}
                     {% endif %}
@@ -153,7 +153,7 @@
                     {% for page in header_pages %}
                     <a href="/{{ page.slug }}"
                        class="block px-4 py-2 text-gray-700 dark:text-gray-300 hover:bg-gray-100 dark:hover:bg-gray-700 rounded-lg">
-                        {{ page.title }}
+                        {{ page.get_translated_title(current_language|default('fr')) }}
                     </a>
                     {% endfor %}
                 {% endif %}
@@ -195,7 +195,7 @@
                         <li>
                             <a href="/{{ page.slug }}"
                                class="text-gray-600 dark:text-gray-400 hover:text-primary dark:hover:text-primary transition-colors">
-                                {{ page.title }}
+                                {{ page.get_translated_title(current_language|default('fr')) }}
                             </a>
                         </li>
                         {% endfor %}
@@ -208,13 +208,13 @@
             <div class="mt-12 pt-8 border-t border-gray-200 dark:border-gray-700">
                 <div class="flex flex-col md:flex-row justify-between items-center">
                     <p class="text-gray-600 dark:text-gray-400 text-sm">
-                        &copy; {{ current_year }} {{ platform.name if platform else 'Wizard' }}. All rights reserved.
+                        &copy; {{ current_year }} {{ platform.name if platform else 'Wizard' }}. {{ _("cms.platform.footer.all_rights_reserved") }}
                     </p>
                     <div class="flex space-x-6 mt-4 md:mt-0">
                         {% if legal_pages %}
                             {% for page in legal_pages %}
                             <a href="/{{ page.slug }}" class="text-gray-600 dark:text-gray-400 hover:text-primary text-sm transition-colors">
-                                {{ page.title }}
+                                {{ page.get_translated_title(current_language|default('fr')) }}
                             </a>
                             {% endfor %}
                         {% else %}