refactor: implement module-driven permissions and relocate business logic

File Relocations:
- Delete app/config/ folder (empty after menu_registry removal)
- Move feature_gate.py → app/modules/billing/dependencies/
- Move theme_presets.py → app/modules/cms/services/

Module-Driven Permissions System:
- Add PermissionDefinition dataclass to app/modules/base.py
- Create PermissionDiscoveryService in tenancy module
- Update module definitions to declare their own permissions:
  - core: dashboard.view, settings.*
  - catalog: products.*
  - orders: orders.*
  - inventory: stock.*
  - customers: customers.*
  - tenancy: team.*
- Update app/core/permissions.py to use discovery service
- Role presets (owner, manager, staff, etc.) now use module permissions

This follows the same pattern as module-driven menus:
- Each module defines its permissions in definition.py
- PermissionDiscoveryService aggregates all permissions at runtime
- Tenancy module handles role-to-permission assignment

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

app/modules/inventory/definition.py

@@ -6,7 +6,12 @@ Defines the inventory module including its features, menu items,
 route configurations, and self-contained module settings.
 """
 
-from app.modules.base import MenuItemDefinition, MenuSectionDefinition, ModuleDefinition
+from app.modules.base import (
+    MenuItemDefinition,
+    MenuSectionDefinition,
+    ModuleDefinition,
+    PermissionDefinition,
+)
 from app.modules.enums import FrontendType
 
 
@@ -33,6 +38,27 @@ inventory_module = ModuleDefinition(
         "transaction history, and bulk imports."
     ),
     version="1.0.0",
+    # Module-driven permissions
+    permissions=[
+        PermissionDefinition(
+            id="stock.view",
+            label_key="inventory.permissions.stock_view",
+            description_key="inventory.permissions.stock_view_desc",
+            category="stock",
+        ),
+        PermissionDefinition(
+            id="stock.edit",
+            label_key="inventory.permissions.stock_edit",
+            description_key="inventory.permissions.stock_edit_desc",
+            category="stock",
+        ),
+        PermissionDefinition(
+            id="stock.transfer",
+            label_key="inventory.permissions.stock_transfer",
+            description_key="inventory.permissions.stock_transfer_desc",
+            category="stock",
+        ),
+    ],
     features=[
         "inventory_basic",  # Basic stock tracking
         "inventory_locations",  # Multiple warehouse locations