Template
* remove toggle_source_view plugin and related command implementations * drop built-in sibling focus/move commands from core * simplify EditorsContainer (Paned → Box) and editor initialization * refactor source view creation to return (scrolled_window, source_view) * add source view lifecycle events (remove/removed) * rename GetNewCommandSystemEvent → CreateCommandSystemEvent * update CommandsController to handle command system creation and cleanup * ensure command systems are removed with their source views * improve focus border handling across sibling chains * clean up imports to use absolute core.* paths * update keybindings to remove deprecated split navigation commands