feat(storefront): section-based homepages, header action partials, fixes

Phase 1 — Section-based store homepages:
- Store defaults use template="full" with per-platform sections JSON
- OMS: shop hero + features + CTA; Loyalty: rewards hero + features + CTA
- Hosting: services hero + features + CTA
- Deep placeholder resolution for {{store_name}} inside sections JSON
- landing-full.html uses resolved page_sections from context

Phase 2 — Module-contributed header actions:
- header_template field on MenuItemDefinition + DiscoveredMenuItem
- Catalog provides header-search.html partial
- Cart provides header-cart.html partial with badge
- Base template iterates storefront_nav.actions with {% include %}
- Generic icon fallback for actions without a template

Fixes:
- Store theme API: get_store_by_code → get_store_by_code_or_subdomain

Docs:
- CMS redesign proposal: menu restructure, page types, translations UI

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/cms/services/content_page_service.py

@@ -24,6 +24,7 @@ Lookup Strategy for Store Storefronts:
 
 import logging
 from datetime import UTC, datetime
+from typing import Any
 
 from sqlalchemy import and_
 from sqlalchemy.orm import Session
@@ -991,6 +992,28 @@ class ContentPageService:
             content = content.replace(placeholder, value)
         return content
 
+    @staticmethod
+    def resolve_placeholders_deep(data, store) -> Any:
+        """
+        Recursively resolve {{store_name}} etc. in a nested data structure
+        (dicts, lists, strings). Used for sections JSON in store default pages.
+        """
+        if not data or not store:
+            return data
+        if isinstance(data, str):
+            return ContentPageService.resolve_placeholders(data, store)
+        if isinstance(data, dict):
+            return {
+                k: ContentPageService.resolve_placeholders_deep(v, store)
+                for k, v in data.items()
+            }
+        if isinstance(data, list):
+            return [
+                ContentPageService.resolve_placeholders_deep(item, store)
+                for item in data
+            ]
+        return data
+
     # =========================================================================
     # Homepage Sections Management
     # =========================================================================

app/modules/cms/services/store_theme_service.py

@@ -70,7 +70,7 @@ class StoreThemeService:
         """
         from app.modules.tenancy.services.store_service import store_service
 
-        store = store_service.get_store_by_code(db, store_code)
+        store = store_service.get_store_by_code_or_subdomain(db, store_code)
 
         if not store:
             self.logger.warning(f"Store not found: {store_code}")