Interaction · Pointer: resize, turn, band selection, and gpui's own drag

Resizable sizes a box from its right and bottom edges and a grip at
its corner, within its least and greatest size; the grip is a Tab stop
whose arrows resize a step. Rotatable turns an svg to its angle inside
a ring whose knob a drag moves, Shift snapping to 15 degrees, with the
arrows turning it a notch. SelectionArea selects items with a band
drawn on empty space, a press, Command or Shift to add, and a cursor
the arrows walk with Space to add or drop; Escape clears and
Command-A takes all. The gallery shows gpui's own drag and drop, drag
preview, double press and wheel zoom, with pointers for Sortable,
LongPress and PanZoom; pinch stays blocked, gpui 0.2.2 forwards no
magnify event.

TASKS.md

@@ -130,7 +130,8 @@ Per-component lines live in `tasks/`. Tags there:
 - [x] T36c Account · Billing and team — `tasks/ch31-43.md`
 - [x] T37a Onboarding · Flows and highlights — `tasks/ch31-43.md`
 - [x] T37b Onboarding · Help — `tasks/ch31-43.md`
-- [ ] T38 Interaction
+- [ ] T38a Interaction · Pointer
+- [ ] T38b Interaction · Keys, scroll and focus
 - [ ] T39 Theme
 - [ ] T40 i18n & a11y
 - [ ] T41 Maps