Add file deletion detection, WebKit improvements, and bug fixes

- Add FileExternallyDeletedEvent with UI indicator in tabs for deleted files
- Set minimum height (300px) for editors container
- Add Developer Tools to WebKit context menu
- Fix DnD URI handling when uris list is empty
- Fix buffer replacement using freeze_notify and proper bounds handling
- Move webkit_ui_settings to new path
- Remove <change_me> placeholders from APP_NAME and user config

user_config/usr/applications/change_me.desktop

@@ -0,0 +1,11 @@
+[Desktop Entry]
+Name=<change_me>
+GenericName=<change_me>
+Comment=<change_me>
+Exec=/bin/<change_me> %F
+Icon=/usr/share/<change_me>/icons/<change_me>.png
+Type=Application
+StartupNotify=true
+Categories=System;FileTools;Utility;Core;GTK;FileManager;
+MimeType=
+Terminal=false