refactor(editor): remove legacy split-view system and introduce source view lifecycle

* 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

src/libs/dto/code/events/__init__.py

@@ -7,6 +7,8 @@ from .code_event import CodeEvent
 from .toggle_plugins_ui_event import TogglePluginsUiEvent
 from .create_source_view_event import CreateSourceViewEvent
 from .created_source_view_event import CreatedSourceViewEvent
+from .remove_source_view_event import RemoveSourceViewEvent
+from .removed_source_view_event import RemovedSourceViewEvent
 from .register_completer_event import RegisterCompleterEvent
 from .unregister_completer_event import UnregisterCompleterEvent
 from .register_provider_event import RegisterProviderEvent
@@ -21,7 +23,7 @@ from .filter_out_loaded_files_event import FilterOutLoadedFilesEvent
 from .get_active_view_event import GetActiveViewEvent
 from .get_source_views_event import GetSourceViewsEvent
 
-from .get_new_command_system_event import GetNewCommandSystemEvent
+from .create_command_system_event import CreateCommandSystemEvent
 from .request_completion_event import RequestCompletionEvent
 from .cursor_moved_event import CursorMovedEvent
 from .modified_changed_event import ModifiedChangedEvent

src/libs/dto/code/events/create_command_system_event.py

@@ -9,5 +9,5 @@ from .code_event import CodeEvent
 
 
 @dataclass
-class GetNewCommandSystemEvent(CodeEvent):
+class CreateCommandSystemEvent(CodeEvent):
     ...

src/libs/dto/code/events/remove_source_view_event.py

@@ -0,0 +1,14 @@
+# Python imports
+from dataclasses import dataclass
+
+# Lib imports
+
+# Application imports
+from .code_event import CodeEvent
+from libs.dto.states.source_view_states import SourceViewStates
+
+
+
+@dataclass
+class RemoveSourceViewEvent(CodeEvent):
+    ...

src/libs/dto/code/events/removed_source_view_event.py

@@ -0,0 +1,14 @@
+# Python imports
+from dataclasses import dataclass
+
+# Lib imports
+
+# Application imports
+from .code_event import CodeEvent
+from libs.dto.states.source_view_states import SourceViewStates
+
+
+
+@dataclass
+class RemovedSourceViewEvent(CodeEvent):
+    ...