feat(i18n): add multilingual platform descriptions and HostWizard demo data

- Add description_translations JSON column to Platform model + migration
- Add language tabs to platform admin edit form for multilingual descriptions
- Update API schemas to include description_translations in request/response
- Translate pricing section UI labels via _t() macro (monthly/annual/CTA/etc.)
- Add Luxembourgish (lb) support to all platforms (OMS, Main, Loyalty, Hosting)
- Seed description_translations, contact emails, and social links for all platforms
- Add LuxWeb Agency demo merchant with hosting stores, team, and content pages
- Fix language code typo: lu → lb in platform-edit.js availableLanguages
- Fix store content pages to use correct primary platform instead of hardcoded OMS

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

app/modules/tenancy/models/platform.py

@@ -71,6 +71,13 @@ class Platform(Base, TimestampMixin):
         comment="Platform description for admin/marketing purposes",
     )
 
+    description_translations = Column(
+        JSON,
+        nullable=True,
+        default=None,
+        comment="Language-keyed description dict for multi-language support",
+    )
+
     # ========================================================================
     # Domain Routing
     # ========================================================================
@@ -226,6 +233,17 @@ class Platform(Base, TimestampMixin):
     # Properties
     # ========================================================================
 
+    def get_translated_description(self, lang: str, default_lang: str = "fr") -> str:
+        """Return description in the requested language with fallback."""
+        if self.description_translations:
+            return (
+                self.description_translations.get(lang)
+                or self.description_translations.get(default_lang)
+                or self.description
+                or ""
+            )
+        return self.description or ""
+
     @property
     def base_url(self) -> str:
         """Get the base URL for this platform (for link generation)."""