* feat(web): drag-reorder subtasks within a parent task
Adds per-parent subtask ordering in the sidebar. Drag a subtask under its
parent to reorder; the chosen order is independent of the global sort and
persists per browser via localStorage.
- New `sidebarTaskPrefs.subtaskOrderByParentId` slice field and matching
`setSubtaskOrder(parentId, ids)` action, persisted to localStorage under
`kandev.sidebar.subtaskOrderByParentId`.
- `applyView` applies the per-parent override after `separateSubtasks`, so
it never touches root order or the active sort spec.
- TaskSwitcher exposes `onReorderSubtasks(parentId, ids)`; each parent's
subtask list lives in its own nested DndContext / SortableContext using
the existing dnd-kit setup.
- Task-deletion cleanup strips the deleted id as both parent key and
subtask entry from `subtaskOrderByParentId` in store + localStorage.
* refactor(web): address PR review feedback on subtask reordering
- Extract `pruneSubtaskOrder(map, taskId)` helper in `local-storage.ts`;
use it in both `cleanupTaskStorage` and `removeTaskFromSidebarPrefs`
to keep the two cleanup paths in lockstep.
- Move `SortableSubtaskRow`, `SortableSubtaskList`, and `useSubtaskDnd`
into a new sibling file `task-switcher-subtask-dnd.tsx` so the
switcher stays under the 600-line soft limit.
- `SortableSubtaskList` now short-circuits to a plain row map when
`onReorderSubtasks` is undefined — read-only callers no longer get a
misleading grab cursor or unused DnD scaffolding.
* fix(web): add stable keys to non-DnD subtask render path
When `onReorderSubtasks` is undefined, the early-return branch in
`SortableSubtaskList` mapped subtasks without keys, falling back to
React's index-based reconciliation. Wrap each child in a keyed
`Fragment` so reorders or size changes reconcile correctly.
* refactor(web): single-source DRAG_ACTIVATION_DISTANCE
Export the constant from `task-switcher-subtask-dnd.tsx` and import it
in `task-switcher.tsx` instead of declaring the same value twice.
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Co-authored-by: Kandev Agent <agent@kandev.dev>
Carlos Florêncio