refactor: remove split_pane_manager plugin and harden view handling

- Delete deprecated split_pane_manager command plugin and all related commands
- Introduce new split_pane command structure (untracked replacement)
- Add guard in code_minimap to handle missing active view
- Prevent language detection for non-file buffers in command_helpers

This cleans up legacy split pane logic and improves stability for edge cases.

plugins/code/ui/code_minimap/plugin.py

@@ -30,6 +30,7 @@ class Plugin(PluginCode):
 
         event = Event_Factory.create_event("get_active_view")
         self.emit_to("source_views", event)
+        if not event.response: return
         code_minimap.set_smini_view(event.response)
 
     def unload(self):