Sortable enhancements

# Feature request
Enhance the functionality of the Sortable component.

**Nice to haves/suggestions**
- When dragging a row a dotted outline of its dropped placement should the drag be ended could be shown.

**Stretch Tasks**
- Add the option for a `` popover for removing items.
- Introduce support for table rows.
- Add support for disabling individual items.

Locate the Sortable component and read its docs/examples and tests to understand current props and drag lifecycle. Inspect how remove actions and item rendering are implemented, since those paths are where confirmation, table-row mode, and disabled-item behavior would be added. Run Sortable tests/examples, and mark the issue done when a drop-placement outline, optional confirmation popover, table-row support, and per-item disabling are implemented and demonstrably working.

索引モデルが issue の本文から書いたものです。