refactor: remove all backward compatibility code across 70 files

Clean up 28 backward compatibility instances identified in the codebase.
The app is not live, so all shims are replaced with the target architecture:

- Remove legacy Inventory.location column (use bin_location exclusively)
- Remove dashboard _extract_metric_value helper (use flat metrics dict)
- Remove legacy stat field duplicates (total_stores, total_imports, etc.)
- Remove 13 re-export shims and class aliases across modules
- Remove module-enabling JSON fallback (use PlatformModule junction table)
- Remove menu_to_legacy_format() conversion (return dataclasses directly)
- Remove title/description from MarketplaceProductBase schema
- Clean billing convenience method docstrings
- Clean test fixtures and backward-compat comments
- Add PlatformModule seeding to init_production.py

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

app/modules/tenancy/models/admin.py

@@ -57,9 +57,6 @@ class AdminAuditLog(Base, TimestampMixin):
         return f"<AdminAuditLog(id={self.id}, action='{self.action}', target={self.target_type}:{self.target_id})>"
 
 
-# AdminNotification has been moved to app/modules/messaging/models/admin_notification.py
-# It's re-exported via models/database/__init__.py for backwards compatibility
-
 
 class AdminSetting(Base, TimestampMixin):
     """

app/modules/tenancy/models/merchant_domain.py

@@ -9,7 +9,7 @@ Individual stores can optionally override this with their own custom StoreDomain
 Domain Resolution Priority:
 1. Store-specific custom domain (StoreDomain) -> highest priority
 2. Merchant domain (MerchantDomain) -> inherited default
-3. Store subdomain ({store.subdomain}.loyalty.lu) -> fallback
+3. Store subdomain ({store.subdomain}.rewardflow.lu) -> fallback
 """
 
 from sqlalchemy import (

app/modules/tenancy/models/platform.py

@@ -80,7 +80,7 @@ class Platform(Base, TimestampMixin):
         unique=True,
         nullable=True,
         index=True,
-        comment="Production domain (e.g., 'oms.lu', 'loyalty.lu')",
+        comment="Production domain (e.g., 'omsflow.lu', 'rewardflow.lu')",
     )
 
     path_prefix = Column(

app/modules/tenancy/models/platform_module.py

@@ -6,9 +6,6 @@ This junction table provides:
 - Auditability: Track when modules were enabled/disabled and by whom
 - Configuration: Per-module settings specific to each platform
 - State tracking: Explicit enabled/disabled states with timestamps
-
-Replaces the simpler Platform.settings["enabled_modules"] JSON approach
-for better auditability and query capabilities.
 """
 
 from sqlalchemy import (