Upgrade MyGo to v0.5.5

MyGo v0.5.5 returns ui.Element as a checked value handle instead of a
pointer. Migrated with `mygo migrate-ui`, then fixed what the codemod
leaves to review:

- Element nil checks become .Valid(); absent elements are ui.Element{}.
- Input handlers and paint callbacks run outside the build pass, where
  elements expire and Context methods are inert: read IsDisabled into a
  local during the build, keep a ui.Handle for Focus, use c.Services()
  for clipboard access, create ui.Local state during the build.
- Add core.AutoFocus: v0.5.5 records an overlay's opener after its
  content builds, so same-frame autofocus lost focus restore on close.
  It focuses one frame later; cascader rows defer their focus likewise.
- core.OverlayLayer identifies build passes by the root element, not
  c.Now(), which repeats across passes and under the Tester clock.
- Context menus survive the opening press counted as PressedOutside;
  split button tooltip no longer reorders its open menu; disabled
  menubar rows pass presses to the panel; Form defers blur-started
  async checks so the growing message no longer moves Submit away
  from the release; Combobox drops its disabled copy now that MyGo
  blocks typing under a disabled wrapper (canary flipped to a guard).
- The Tester clock is virtual: tests use Advance/Now instead of
  time.Sleep/time.Now and read element state inside the view. The web
  mirror advances the clock to wall time before each frame and input.
- AGENTS.md and docs describe the value Element API and the new pin.

Snapshot goldens are darwin-only and were not re-verified here.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

project/label_manager.go

@@ -81,7 +81,7 @@ func LabelManager(c *ui.Context, labels *[]TaskLabel, selected *[]string, opts L
 		removed := -1
 		ui.List(c, state, len(*labels), func(i int) {
 			l := &(*labels)[i]
-			ui.Row(c).Key(l.ID).MinHeight(d.ControlHeight()).Gap(d.Unit() * 2).AlignItems(ui.Center).Children(func() {
+			ui.Row(c.Key(l.ID)).MinHeight(d.ControlHeight()).Gap(d.Unit() * 2).AlignItems(ui.Center).Children(func() {
 				on := cache.selected[l.ID]
 				box := ui.CheckboxBase(c, &on).Size(theme.MinHitSize, theme.MinHitSize).Center().Label(l.Name)
 				internal.Ring(box, k.Focus, theme.ControlRadius)
@@ -146,7 +146,7 @@ func labelEditRow(c *ui.Context, s *labelManagerState, l *TaskLabel, taken func(
 	d := core.Density(c)
 	ui.Column(c).Grow(1).Gap(d.Unit()).Children(func() {
 		in := input.TextInput(c, &s.name, input.TextInputOptions{Label: core.Msg(c, "label_manager.name"), Error: s.problem})
-		in.Input.AutoFocus()
+		core.AutoFocus(c, in.Input)
 		ui.Row(c).Gap(d.Unit()).Role(ui.RoleRadioGroup).Label(core.Msg(c, "label_manager.color")).Children(func() {
 			for i := range 6 {
 				col := datetime.EventColor(i)