fix: recording save functionality and authentication

- Fix artist_name null handling in header component with email fallback
- Fix authentication in recording endpoints to use req.accountability
- Change duration field type from integer to double precision for millisecond precision
- Add createRecording service function with proper authentication
- Update play page to use fetch API for recording saves

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

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

packages/frontend/src/lib/components/header/header.svelte

@@ -127,7 +127,7 @@ function isActiveLink(link: any) {
 
             <LogoutButton
               user={{
-                name: authStatus.user!.artist_name,
+                name: authStatus.user!.artist_name || authStatus.user!.email.split('@')[0] || 'User',
                 avatar: getAssetUrl(authStatus.user!.avatar?.id, 'mini')!,
                 email: authStatus.user!.email
               }}