refactor: migrate modules from re-exports to canonical implementations

Move actual code implementations into module directories:
- orders: 5 services, 4 models, order/invoice schemas
- inventory: 3 services, 2 models, 30+ schemas
- customers: 3 services, 2 models, customer schemas
- messaging: 3 services, 2 models, message/notification schemas
- monitoring: background_tasks_service
- marketplace: 5+ services including letzshop submodule
- dev_tools: code_quality_service, test_runner_service
- billing: billing_service
- contracts: definition.py

Legacy files in app/services/, models/database/, models/schema/
now re-export from canonical module locations for backwards
compatibility. Architecture validator passes with 0 errors.

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

app/modules/dev_tools/services/__init__.py

@@ -2,16 +2,14 @@
 """
 Dev-Tools module services.
 
-This module re-exports services from their current locations.
-In future cleanup phases, the actual service implementations
-may be moved here.
+Provides code quality scanning and test running functionality.
 
 Services:
 - code_quality_service: Code quality scanning and violation management
 - test_runner_service: Test execution and results management
 """
 
-from app.services.code_quality_service import (
+from app.modules.dev_tools.services.code_quality_service import (
     code_quality_service,
     CodeQualityService,
     VALIDATOR_ARCHITECTURE,
@@ -21,7 +19,7 @@ from app.services.code_quality_service import (
     VALIDATOR_SCRIPTS,
     VALIDATOR_NAMES,
 )
-from app.services.test_runner_service import (
+from app.modules.dev_tools.services.test_runner_service import (
     test_runner_service,
     TestRunnerService,
 )