feat: add admin messaging interface

- Add admin messages API endpoints (/api/v1/admin/messages)
- Add admin messages page route (/admin/messages)
- Add messages.html template with split-panel conversation view
- Add messages.js Alpine component for messaging UI
- Add Messages link to admin sidebar under Platform Administration
- Add message icon with unread badge to admin header
- Update init-alpine.js with headerMessages component

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

app/api/v1/admin/__init__.py

@@ -31,11 +31,13 @@ from . import (
     code_quality,
     companies,
     content_pages,
+    customers,
     dashboard,
     inventory,
     letzshop,
     logs,
     marketplace,
+    messages,
     monitoring,
     notifications,
     order_item_exceptions,
@@ -91,6 +93,9 @@ router.include_router(
 # Include user management endpoints
 router.include_router(users.router, tags=["admin-users"])
 
+# Include customer management endpoints
+router.include_router(customers.router, tags=["admin-customers"])
+
 
 # ============================================================================
 # Dashboard & Statistics
@@ -151,6 +156,9 @@ router.include_router(settings.router, tags=["admin-settings"])
 # Include notifications and alerts endpoints
 router.include_router(notifications.router, tags=["admin-notifications"])
 
+# Include messaging endpoints
+router.include_router(messages.router, tags=["admin-messages"])
+
 # Include log management endpoints
 router.include_router(logs.router, tags=["admin-logs"])