## PR description
The previous approach used a detached flag to represent selection mode,
which could was not synced sync with actual UI selection state. This
change ties the edit mode's selection/fallback behavior directly to
whether records are truly selected in the record index.
- Removes `commandMenuItemEditSelectionModeState` (a standalone 'none' |
'selection' atom) and replaces it with
`mainContextStoreHasSelectedRecordsSelector`, which derives selection
state from the real record selection in the context store.
- Adds `useSelectFirstRecordForEditMode` to programmatically select the
first record (table row or kanban card) when toggling to selection mode,
and useResetRecordIndexSelection to clear selection when toggling off or
exiting edit mode.
- Ensures record selection is properly cleaned up when exiting layout
customization mode or closing the side panel.
## Video QA
### Table
https://github.com/user-attachments/assets/1d845809-8369-4872-b3a9-a0281b8e464b
### Board
https://github.com/user-attachments/assets/325c2d58-4ca0-408a-ab4a-66b97d9d70de
Raphaël Bosi