feat: complete modular platform architecture (Phases 1-5)

Phase 1 - Vendor Router Integration:
- Wire up vendor module routers in app/api/v1/vendor/__init__.py
- Use lazy imports via __getattr__ to avoid circular dependencies

Phase 2 - Extract Remaining Modules:
- Create 6 new module directories: customers, cms, analytics, messaging,
  dev_tools, monitoring
- Each module has definition.py and route wrappers
- Update registry to import from extracted modules

Phase 3 - Database Table Migration:
- Add PlatformModule junction table for auditable module tracking
- Add migration zc2m3n4o5p6q7_add_platform_modules_table.py
- Add modules relationship to Platform model
- Update ModuleService with JSON-to-junction-table migration

Phase 4 - Module-Specific Configuration UI:
- Add /api/v1/admin/module-config/* endpoints
- Add module-config.html template and JS

Phase 5 - Integration Tests:
- Add tests/fixtures/module_fixtures.py
- Add tests/integration/api/v1/admin/test_modules.py
- Add tests/integration/api/v1/modules/test_module_access.py

Architecture fixes:
- Fix JS-003 errors: use ...data() directly in Alpine components
- Fix JS-005 warnings: add init() guards to prevent duplicate init
- Fix API-001 errors: add MenuActionResponse Pydantic model
- Add FE-008 noqa for dynamic number input in template

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

models/database/__init__.py

@@ -8,6 +8,7 @@ from .admin import (
     AdminSetting,
     PlatformAlert,
 )
+from .admin_menu_config import AdminMenuConfig, FrontendType, MANDATORY_MENU_ITEMS
 from .admin_platform import AdminPlatform
 from .architecture_scan import (
     ArchitectureScan,
@@ -19,6 +20,7 @@ from .base import Base
 from .company import Company
 from .content_page import ContentPage
 from .platform import Platform
+from .platform_module import PlatformModule
 from .vendor_platform import VendorPlatform
 from .customer import Customer, CustomerAddress
 from .password_reset_token import PasswordResetToken
@@ -83,9 +85,12 @@ from .vendor_theme import VendorTheme
 __all__ = [
     # Admin-specific models
     "AdminAuditLog",
+    "AdminMenuConfig",
+    "FrontendType",
     "AdminNotification",
     "AdminPlatform",
     "AdminSetting",
+    "MANDATORY_MENU_ITEMS",
     "PlatformAlert",
     "AdminSession",
     # Architecture/Code Quality
@@ -112,6 +117,7 @@ __all__ = [
     "ContentPage",
     # Platform
     "Platform",
+    "PlatformModule",
     "VendorPlatform",
     # Customer & Auth
     "Customer",