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>

app/api/v1/vendor/__init__.py

@@ -8,6 +8,23 @@ IMPORTANT:
 - This router is for JSON API endpoints only
 - HTML page routes are mounted separately in main.py at /vendor/*
 - Do NOT include pages.router here - it causes route conflicts
+
+MODULE SYSTEM:
+Routes can be module-gated using require_module_access() dependency.
+For multi-tenant apps, module enablement is checked at request time
+based on platform context (not at route registration time).
+
+Extracted modules (app/modules/{module}/routes/):
+- billing: Subscription tiers, vendor billing, invoices
+- inventory: Stock management, inventory tracking
+- orders: Order management, fulfillment, exceptions
+- marketplace: Letzshop integration, product sync
+
+Module extraction pattern:
+1. Create app/modules/{module}/ directory
+2. Create routes/vendor.py with require_module_access("{module}") dependency
+3. Import module router here and include it
+4. Comment out legacy router include
 """
 
 from fastapi import APIRouter
@@ -42,6 +59,15 @@ from . import (
     usage,
 )
 
+# Import extracted module routers
+# NOTE: Import directly from vendor.py files to avoid circular imports through __init__.py
+from app.modules.billing.routes.vendor import vendor_router as billing_vendor_router
+from app.modules.inventory.routes.vendor import vendor_router as inventory_vendor_router
+from app.modules.orders.routes.vendor import vendor_router as orders_vendor_router
+from app.modules.orders.routes.vendor import vendor_exceptions_router as orders_exceptions_router
+from app.modules.marketplace.routes.vendor import vendor_router as marketplace_vendor_router
+from app.modules.marketplace.routes.vendor import vendor_letzshop_router as letzshop_vendor_router
+
 # Create vendor router
 router = APIRouter()
 
@@ -67,14 +93,26 @@ router.include_router(onboarding.router, tags=["vendor-onboarding"])
 
 # Business operations (with prefixes: /products/*, /orders/*, etc.)
 router.include_router(products.router, tags=["vendor-products"])
-router.include_router(orders.router, tags=["vendor-orders"])
-router.include_router(order_item_exceptions.router, tags=["vendor-order-exceptions"])
+
+# Include orders module router (with module access control)
+router.include_router(orders_vendor_router, tags=["vendor-orders"])
+router.include_router(orders_exceptions_router, tags=["vendor-order-exceptions"])
+# Legacy: router.include_router(orders.router, tags=["vendor-orders"])
+# Legacy: router.include_router(order_item_exceptions.router, tags=["vendor-order-exceptions"])
+
 router.include_router(invoices.router, tags=["vendor-invoices"])
 router.include_router(customers.router, tags=["vendor-customers"])
 router.include_router(team.router, tags=["vendor-team"])
-router.include_router(inventory.router, tags=["vendor-inventory"])
-router.include_router(marketplace.router, tags=["vendor-marketplace"])
-router.include_router(letzshop.router, tags=["vendor-letzshop"])
+
+# Include inventory module router (with module access control)
+router.include_router(inventory_vendor_router, tags=["vendor-inventory"])
+# Legacy: router.include_router(inventory.router, tags=["vendor-inventory"])
+
+# Include marketplace module router (with module access control)
+router.include_router(marketplace_vendor_router, tags=["vendor-marketplace"])
+router.include_router(letzshop_vendor_router, tags=["vendor-letzshop"])
+# Legacy: router.include_router(marketplace.router, tags=["vendor-marketplace"])
+# Legacy: router.include_router(letzshop.router, tags=["vendor-letzshop"])
 
 # Services (with prefixes: /payments/*, /media/*, etc.)
 router.include_router(payments.router, tags=["vendor-payments"])
@@ -82,7 +120,11 @@ router.include_router(media.router, tags=["vendor-media"])
 router.include_router(notifications.router, tags=["vendor-notifications"])
 router.include_router(messages.router, tags=["vendor-messages"])
 router.include_router(analytics.router, tags=["vendor-analytics"])
-router.include_router(billing.router, tags=["vendor-billing"])
+
+# Include billing module router (with module access control)
+router.include_router(billing_vendor_router, tags=["vendor-billing"])
+# Legacy: router.include_router(billing.router, tags=["vendor-billing"])
+
 router.include_router(features.router, tags=["vendor-features"])
 router.include_router(usage.router, tags=["vendor-usage"])