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/migrations/versions/tenancy_004_add_platform_description_translations.py

@@ -0,0 +1,31 @@
+"""add description_translations to platforms
+
+Revision ID: tenancy_004
+Revises: billing_002
+Create Date: 2026-03-04
+"""
+
+import sqlalchemy as sa
+
+from alembic import op
+
+revision = "tenancy_004"
+down_revision = "billing_002"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "platforms",
+        sa.Column(
+            "description_translations",
+            sa.JSON(),
+            nullable=True,
+            comment="Language-keyed description dict for multi-language support",
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("platforms", "description_translations")