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/analytics/routes/api/vendor.py

@@ -16,7 +16,7 @@ from fastapi import APIRouter, Depends, Query
 from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_vendor_api, get_db, require_module_access
-from app.core.feature_gate import RequireFeature
+from app.modules.billing.dependencies.feature_gate import RequireFeature
 from app.modules.analytics.services import stats_service
 from app.modules.analytics.schemas import (
     VendorAnalyticsCatalog,