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/routes/api/admin_platforms.py

@@ -41,6 +41,7 @@ class PlatformResponse(BaseModel):
     code: str
     name: str
     description: str | None = None
+    description_translations: dict[str, str] | None = None
     domain: str | None = None
     path_prefix: str | None = None
     logo: str | None = None
@@ -76,6 +77,7 @@ class PlatformUpdateRequest(BaseModel):
 
     name: str | None = None
     description: str | None = None
+    description_translations: dict[str, str] | None = None
     domain: str | None = None
     path_prefix: str | None = None
     logo: str | None = None
@@ -115,6 +117,7 @@ def _build_platform_response(db: Session, platform) -> PlatformResponse:
         code=platform.code,
         name=platform.name,
         description=platform.description,
+        description_translations=platform.description_translations,
         domain=platform.domain,
         path_prefix=platform.path_prefix,
         logo=platform.logo,