feat: add module-specific locale support for i18n

Enhance the self-contained module architecture with locale/translation support:

ModuleDefinition changes:
- Add locales_path attribute for module-specific translations
- Add get_locales_dir() helper method
- Include locales in validate_structure() check

i18n module changes (app/utils/i18n.py):
- Add get_module_locale_dirs() to discover module locales
- Update load_translations() to merge module translations with core
- Module translations namespaced under module code (e.g., cms.title)
- Add _deep_merge() helper for nested dictionary merging
- Add _load_json_file() helper for cleaner JSON loading

CMS module locales:
- Add app/modules/cms/locales/ with translations for all 4 languages
- en.json, fr.json, de.json, lb.json with CMS-specific strings
- Covers: pages, page editing, SEO, navigation, publishing, homepage
  sections, media library, themes, actions, and messages

Usage in templates:
  {{ _("cms.title") }}           -> "Content Management" (en)
  {{ _("cms.pages.create") }}    -> "Créer une page" (fr)
  {{ _("cms.publishing.draft") }} -> "Entwurf" (de)

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

app/modules/cms/locales/en.json

@@ -0,0 +1,126 @@
+{
+  "title": "Content Management",
+  "description": "Manage content pages, media library, and vendor themes",
+  "pages": {
+    "title": "Content Pages",
+    "subtitle": "Manage platform and vendor content pages",
+    "create": "Create Page",
+    "edit": "Edit Page",
+    "delete": "Delete Page",
+    "list": "All Pages",
+    "empty": "No pages found",
+    "empty_search": "No pages match your search",
+    "create_first": "Create First Page"
+  },
+  "page": {
+    "title": "Page Title",
+    "slug": "Slug",
+    "slug_help": "URL-safe identifier (lowercase, numbers, hyphens only)",
+    "content": "Content",
+    "content_format": "Content Format",
+    "format_html": "HTML",
+    "format_markdown": "Markdown",
+    "platform": "Platform",
+    "vendor_override": "Vendor Override",
+    "vendor_override_none": "None (Platform Default)",
+    "vendor_override_help_default": "This is a platform-wide default page",
+    "vendor_override_help_vendor": "This page overrides the default for selected vendor only"
+  },
+  "tiers": {
+    "platform": "Platform Marketing",
+    "vendor_default": "Vendor Default",
+    "vendor_override": "Vendor Override"
+  },
+  "seo": {
+    "title": "SEO & Metadata",
+    "meta_description": "Meta Description",
+    "meta_description_help": "characters (150-160 recommended)",
+    "meta_keywords": "Meta Keywords",
+    "meta_keywords_placeholder": "keyword1, keyword2, keyword3"
+  },
+  "navigation": {
+    "title": "Navigation & Display",
+    "display_order": "Display Order",
+    "display_order_help": "Lower = first",
+    "show_in_header": "Show in Header",
+    "show_in_footer": "Show in Footer",
+    "show_in_legal": "Show in Legal",
+    "show_in_legal_help": "Bottom bar next to copyright"
+  },
+  "publishing": {
+    "published": "Published",
+    "draft": "Draft",
+    "publish_help": "Make this page visible to the public"
+  },
+  "homepage": {
+    "title": "Homepage Sections",
+    "subtitle": "Multi-language content",
+    "loading": "Loading sections...",
+    "hero": {
+      "title": "Hero Section",
+      "badge_text": "Badge Text",
+      "main_title": "Title",
+      "subtitle": "Subtitle",
+      "buttons": "Buttons",
+      "add_button": "Add Button"
+    },
+    "features": {
+      "title": "Features Section",
+      "section_title": "Section Title",
+      "cards": "Feature Cards",
+      "add_card": "Add Feature Card",
+      "icon": "Icon name",
+      "feature_title": "Title",
+      "feature_description": "Description"
+    },
+    "pricing": {
+      "title": "Pricing Section",
+      "section_title": "Section Title",
+      "use_tiers": "Use subscription tiers from database",
+      "use_tiers_help": "When enabled, pricing cards are dynamically pulled from your subscription tier configuration."
+    },
+    "cta": {
+      "title": "Call to Action Section",
+      "main_title": "Title",
+      "subtitle": "Subtitle",
+      "buttons": "Buttons",
+      "add_button": "Add Button"
+    }
+  },
+  "media": {
+    "title": "Media Library",
+    "upload": "Upload",
+    "upload_file": "Upload File",
+    "delete": "Delete",
+    "empty": "No media files",
+    "upload_first": "Upload your first file"
+  },
+  "themes": {
+    "title": "Vendor Themes",
+    "subtitle": "Manage vendor theme customizations"
+  },
+  "actions": {
+    "save": "Save",
+    "saving": "Saving...",
+    "update": "Update Page",
+    "create": "Create Page",
+    "cancel": "Cancel",
+    "back_to_list": "Back to List",
+    "preview": "Preview",
+    "revert_to_default": "Revert to Default"
+  },
+  "messages": {
+    "created": "Page created successfully",
+    "updated": "Page updated successfully",
+    "deleted": "Page deleted successfully",
+    "reverted": "Reverted to default page",
+    "error_loading": "Error loading page",
+    "error_saving": "Error saving page",
+    "confirm_delete": "Are you sure you want to delete this page?"
+  },
+  "filters": {
+    "all_pages": "All Pages",
+    "all_platforms": "All Platforms",
+    "search_placeholder": "Search pages..."
+  }
+}