v1.21.0

Animate dock reorder and fix the folder's broken reorder animation

Dock: pushing icons aside to make room now gets the same live, dwell-
based preview (260ms) and spring animation as the home grid, instead
of icons jumping straight to their new slot with no transition.

Folder: the reorder animation added earlier looked like it worked in
code but icons actually teleported in practice, because each grid slot
was keyed by its index instead of the app's id - Compose just reused
the slot and swapped which icon it drew, instead of sliding the same
icon's own animated position to its new index. Now keyed by id, with
the same 260ms hover dwell as everywhere else before it reorders.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KanGnvgaQn2Pg84pfu3TUM