refactor: migrate remaining routes to modules and enforce auto-discovery

MIGRATION:
- Delete app/api/v1/vendor/analytics.py (duplicate - analytics module already auto-discovered)
- Move usage routes from app/api/v1/vendor/usage.py to billing module
- Move onboarding routes from app/api/v1/vendor/onboarding.py to marketplace module
- Move features routes to billing module (admin + vendor)
- Move inventory routes to inventory module (admin + vendor)
- Move marketplace/letzshop routes to marketplace module
- Move orders routes to orders module
- Delete legacy letzshop service files (moved to marketplace module)

DOCUMENTATION:
- Add docs/development/migration/module-autodiscovery-migration.md with full migration history
- Update docs/architecture/module-system.md with Entity Auto-Discovery Reference section
- Add detailed sections for each entity type: routes, services, models, schemas, tasks,
  exceptions, templates, static files, locales, configuration

ARCHITECTURE VALIDATION:
- Add MOD-016: Routes must be in modules, not app/api/v1/
- Add MOD-017: Services must be in modules, not app/services/
- Add MOD-018: Tasks must be in modules, not app/tasks/
- Add MOD-019: Schemas must be in modules, not models/schema/
- Update scripts/validate_architecture.py with _validate_legacy_locations method
- Update .architecture-rules/module.yaml with legacy location rules

These rules enforce that all entities must be in self-contained modules.
Legacy locations now trigger ERROR severity violations.

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

app/api/v1/vendor/__init__.py

@@ -15,10 +15,11 @@ For multi-tenant apps, module enablement is checked at request time
 based on platform context (not at route registration time).
 
 Self-contained modules (auto-discovered from app/modules/{module}/routes/api/vendor.py):
-- billing: Subscription tiers, vendor billing, checkout, add-ons, features
+- analytics: Vendor analytics and reporting
+- billing: Subscription tiers, vendor billing, checkout, add-ons, features, usage
 - inventory: Stock management, inventory tracking
 - orders: Order management, fulfillment, exceptions, invoices
-- marketplace: Letzshop integration, product sync
+- marketplace: Letzshop integration, product sync, onboarding
 - catalog: Vendor product catalog management
 - cms: Content pages management
 - customers: Customer management
@@ -29,7 +30,6 @@ from fastapi import APIRouter
 
 # Import all sub-routers (legacy routes that haven't been migrated to modules)
 from . import (
-    analytics,
     auth,
     dashboard,
     email_settings,
@@ -38,11 +38,9 @@ from . import (
     media,
     messages,
     notifications,
-    onboarding,
     profile,
     settings,
     team,
-    usage,
 )
 
 # Create vendor router
@@ -66,7 +64,6 @@ router.include_router(profile.router, tags=["vendor-profile"])
 router.include_router(settings.router, tags=["vendor-settings"])
 router.include_router(email_templates.router, tags=["vendor-email-templates"])
 router.include_router(email_settings.router, tags=["vendor-email-settings"])
-router.include_router(onboarding.router, tags=["vendor-onboarding"])
 
 # Business operations (with prefixes: /team/*)
 router.include_router(team.router, tags=["vendor-team"])
@@ -75,8 +72,6 @@ router.include_router(team.router, tags=["vendor-team"])
 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(usage.router, tags=["vendor-usage"])
 
 
 # ============================================================================