chore: update API routers, validation, and docs for module system

- app/api/v1/admin/__init__.py: Updated router imports
- app/api/v1/vendor/__init__.py: Updated router imports
- app/exceptions/code_quality.py: Added module exception imports
- scripts/validate_architecture.py: Added module validation rules
- .architecture-rules/_main.yaml: Include module.yaml rules
- docs/proposals/module-migration-plan.md: Updated migration status

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

.architecture-rules/_main.yaml

@@ -48,6 +48,7 @@ includes:
   - quality.yaml
   - money.yaml
   - migration.yaml
+  - module.yaml
 
 # ============================================================================
 # VALIDATION SEVERITY LEVELS