feat: add module definition completeness validation and permissions

Add new validation rules MOD-020 to MOD-023 for module definition
completeness and standardize permissions across all modules.

Changes:
- Add MOD-020: Module definitions must have required attributes
- Add MOD-021: Modules with menus should have features
- Add MOD-022: Feature modules should have permissions
- Add MOD-023: Modules with routers should use get_*_with_routers pattern

Module permissions added:
- analytics: view, export, manage_dashboards
- billing: view_tiers, manage_tiers, view_subscriptions, manage_subscriptions, view_invoices
- cart: view, manage
- checkout: view_settings, manage_settings
- cms: view_pages, manage_pages, view_media, manage_media, manage_themes
- loyalty: view_programs, manage_programs, view_rewards, manage_rewards
- marketplace: view_integration, manage_integration, sync_products
- messaging: view_messages, send_messages, manage_templates
- payments: view_gateways, manage_gateways, view_transactions

Module improvements:
- Complete cart module with features and permissions
- Complete checkout module with features and permissions
- Add features to catalog module
- Add version to cms module
- Fix loyalty platform_router attachment
- Add path definitions to payments module
- Remove empty scheduled_tasks from dev_tools module

Documentation:
- Update module-system.md with new validation rules
- Update architecture-rules.md with MOD-020 to MOD-023

Tests:
- Add unit tests for module definition completeness
- Add tests for permission structure validation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/modules/checkout/definition.py

@@ -1,7 +1,13 @@
 # app/modules/checkout/definition.py
-"""Checkout module definition."""
+"""
+Checkout module definition.
+
+This module handles the checkout flow, converting cart contents into orders.
+Orchestrates payment processing and order creation.
+"""
+
+from app.modules.base import ModuleDefinition, PermissionDefinition
 
-from app.modules.base import ModuleDefinition
 
 module = ModuleDefinition(
     code="checkout",
@@ -10,4 +16,29 @@ module = ModuleDefinition(
     version="1.0.0",
     is_self_contained=True,
     requires=["cart", "orders", "payments", "customers"],
+    features=[
+        "checkout_flow",  # Multi-step checkout process
+        "order_creation",  # Create orders from cart
+        "payment_processing",  # Payment integration during checkout
+        "checkout_validation",  # Address, inventory, payment validation
+        "guest_checkout",  # Allow checkout without account
+    ],
+    # Note: Checkout is primarily storefront functionality.
+    # These permissions are for admin access to checkout settings.
+    permissions=[
+        PermissionDefinition(
+            id="checkout.view_settings",
+            label_key="checkout.permissions.view_settings",
+            description_key="checkout.permissions.view_settings_desc",
+            category="checkout",
+        ),
+        PermissionDefinition(
+            id="checkout.manage_settings",
+            label_key="checkout.permissions.manage_settings",
+            description_key="checkout.permissions.manage_settings_desc",
+            category="checkout",
+        ),
+    ],
+    # Checkout is storefront-only - no admin/vendor menus needed
+    menu_items={},
 )