Bulk delete (and optional bulk edit) for GroupListView

[d-ryan-ashcraft]

Summary

Add a bulk-delete affordance to GroupListView / GroupManagerView. Deleting a group is currently three clicks per group (row menu → Delete → confirm), which adds up when clearing out several groups.

Motivation

Raised in review of #47 (comment by @epwilkins):

a bulk delete would be nice given it's 3 clicks to delete a group. It's a rare action so probably wouldn't need to be a dominant part of the UI, but the functionality would be helpful. Even rarer, but maybe worth considering would be a bulk edit. Thinking about it though, the only thing you'd really "bulk edit" would be the icon or the color - possibly desirable but not at all critical.

Proposed scope

• Bulk delete: a multi-select mode (e.g. long-press or a selection toggle) that lets the user pick several groups and delete them in one confirmed action. Keep it low-prominence since it's a rare action.
  • Should cascade-unassign like the existing single delete (GroupManagerController.removeGroup).
  • Honor the existing onDelete interception hook so consumers can reconcile with a backend.
• Bulk edit (optional / lower priority): only the icon or color would realistically be bulk-editable. Desirable but not critical — consider only if it falls out cheaply.

Notes

• Out of scope for #46 add group management #47; tracked here as a future iteration.