Update development documentation for silent plugin initialization

- Remove reference to removed 'PayloadCMS Mailing Plugin initialized successfully' log
- Add note explaining that plugin initializes silently on success
- Clarify that absence of errors indicates successful initialization
- Keep documentation aligned with actual plugin behavior
- Bump version to 0.4.3

DEVELOPMENT.md

@@ -126,9 +126,10 @@ When you start the dev server, look for these messages:
 🎯 Test interface will be available at: /mailing-test
 
 ✅ Example email templates created successfully
-PayloadCMS Mailing Plugin initialized successfully
 ```
 
+**Note**: The plugin initializes silently on success (no "initialized successfully" message). If you see no errors, the plugin loaded correctly.
+
 ## Troubleshooting
 
 ### Server won't start