* address TODO item for split_pane_manager plugin and bound keys * add split_pane_manager plugin with create/close split view commands * move sibling focus/move commands from core into plugin system * remove legacy toggle_source_view plugin * redesign EditorsContainer to use simpler Box-based layout * refactor source view API to return (scrolled_window, source_view) * add source view lifecycle events (create/remove/removed) * rename GetNewCommandSystemEvent → CreateCommandSystemEvent * update CommandsController to support command system creation and cleanup * ensure command systems are removed with their source views * improve focus border handling across sibling chains * update telescope integration for new source view structure * clean up container imports and initialization logic * remove old keybindings and align with new split pane workflow
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