Interaction · Pointer: handles inside the box, drags from the press

Resizable's grip sits inside the box's lower right corner and its edge
handles lie inside the edges, their lines on the edge; the edges use
layout::resize_edge, a resize_handle whose line shows only while
hovered, since the box draws its own border. A drag now measures from
the handle's press, kept in keyed state, so the edge follows the
pointer from the first move. Tests drag the right edge downward and
the bottom edge sideways, turn the dial without Shift, and draw a band
with Shift over a selection.

TASKS.md

@@ -414,3 +414,4 @@ Per-component lines live in `tasks/`. Tags there:
 | T37a | 2 | PASS | |
 | T37b | 1 | FAIL | the help panel's rows were bare Tab stops, not a list the keyboard walks; a long support address drew past 280px |
 | T37b | 2 | PASS | |
+| T38a | 1 | FAIL | the resize grip and edge handles hung half outside the box; the edges' sides, a free turn and a band with Shift untested |