Audit keyboard, focus, veils, motion and clocks across all 500

A cross-cutting pass, each fix with a test that failed first.

Veils: MyGo still hands a key to a base that turned off this frame,
so every element key now goes through pixel.Shortcut, which an
archtest enforces. Input handlers record and the build applies them
only while enabled; the editor turns away a veil-frame letter or
copy; value bases get a copy and keep only enabled turns. Popups
give a held focus back to their opener when the veil lifts.

Motion: S5 is enforced at the clock. Every Tick, Since, Step,
Toward and Shot runs at 4-15 fps; blinks keep 1 Hz on 4 fps steps,
fast animations step at 15, and drawn time is quantized to frames.

Clocks stepping back: Since holds at zero without overflow, and
k.Elapsed moves a stored start to now, so nothing goes negative,
runs backward or indexes out of range.

Also: logs count typed text instead of holding it, gallery names
use glyphs the font has, removable rows are keyed, components take
their own Options (archtest), and sweeps over all 508 demos check
veiled keys, clicks, wheels, the clock stepping back and names.

text/scrambletext.go

@@ -11,7 +11,7 @@ const scrambleRunes = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789#$%&*+?"
 type ScrambleTextOptions struct {
 	Slot  pixel.Slot
 	Scale int
-	// FPS is zero for 30; two steps settle a character.
+	// FPS is 4–15, zero for 15; two steps settle one.
 	FPS int
 }
 
@@ -25,7 +25,7 @@ type scrambleState struct {
 // ScrambleText settles from random glyphs to s, left to right.
 func ScrambleText(c *ui.Context, s string, o ScrambleTextOptions) *ui.Element {
 	k, sc := pixel.K(c), scale(o.Scale)
-	fps := pixel.Or("ScrambleText FPS", o.FPS, 30)
+	fps := pixel.Or("ScrambleText FPS", o.FPS, 15)
 	rs := []rune(s)
 	e := ui.Box(c).Size(k.D(pixel.Measure(s)*sc), k.D(pixel.LineHeight*sc)).Label(s).Role(ui.RoleText)
 	st := ui.Local(e, scrambleKey{}, func() scrambleState { return scrambleState{start: -1} })