refactor: migrate messaging and media routes to modules

Messaging module (communication):
- vendor_messages.py: Conversation and message management
- vendor_notifications.py: Vendor notifications
- vendor_email_settings.py: SMTP and provider configuration
- vendor_email_templates.py: Email template customization

CMS module (content management):
- vendor_media.py: Media library management
- vendor_content_pages.py: Content page overrides

All routes auto-discovered via is_self_contained=True.
Deleted 5 legacy files from app/api/v1/vendor/.
app/api/v1/vendor/ now empty except for __init__.py (auto-discovery only).

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

app/modules/messaging/routes/api/vendor.py

@@ -0,0 +1,29 @@
+# app/modules/messaging/routes/api/vendor.py
+"""
+Messaging module vendor API routes.
+
+Aggregates all vendor messaging routes:
+- /messages/* - Conversation and message management
+- /notifications/* - Vendor notifications
+- /email-settings/* - SMTP and provider configuration
+- /email-templates/* - Email template customization
+"""
+
+from fastapi import APIRouter, Depends
+
+from app.api.deps import require_module_access
+
+from .vendor_messages import vendor_messages_router
+from .vendor_notifications import vendor_notifications_router
+from .vendor_email_settings import vendor_email_settings_router
+from .vendor_email_templates import vendor_email_templates_router
+
+vendor_router = APIRouter(
+    dependencies=[Depends(require_module_access("messaging"))],
+)
+
+# Aggregate all messaging vendor routes
+vendor_router.include_router(vendor_messages_router, tags=["vendor-messages"])
+vendor_router.include_router(vendor_notifications_router, tags=["vendor-notifications"])
+vendor_router.include_router(vendor_email_settings_router, tags=["vendor-email-settings"])
+vendor_router.include_router(vendor_email_templates_router, tags=["vendor-email-templates"])