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>

account/workspace_switcher.go

@@ -72,7 +72,7 @@ func WorkspaceSwitcher(c *ui.Context, current *string, spaces []Workspace, opts
 	overlay.Popover(c, b, &st.open, overlay.PopoverOptions{Width: 300, Label: core.Msg(c, "workspace_switcher.label")}, func() {
 		res := input.SearchInput(c, &st.query, input.SearchInputOptions{Placeholder: core.Msg(c, "workspace_switcher.search"), Label: core.Msg(c, "workspace_switcher.search")})
 		in := res.Input
-		in.AutoFocus()
+		core.AutoFocus(c, in)
 		q := strings.ToLower(strings.TrimSpace(st.query))
 		if !st.ready || st.filtered != q || !slices.Equal(st.source, spaces) {
 			st.source, st.filtered, st.ready = slices.Clone(spaces), q, true
@@ -115,10 +115,10 @@ func WorkspaceSwitcher(c *ui.Context, current *string, spaces []Workspace, opts
 }
 
 // workspaceRow displays a clickable workspace with a selection mark.
-func workspaceRow(c *ui.Context, w Workspace, current, cursor bool) *ui.Element {
+func workspaceRow(c *ui.Context, w Workspace, current, cursor bool) ui.Element {
 	k := core.Tokens(c)
 	d := core.Density(c)
-	b := ui.ButtonBase(c).Key(w.ID).MinHeight(d.ControlHeight()).Padding(d.Unit(), d.Unit()*2).Gap(d.Unit() * 2).
+	b := ui.ButtonBase(c.Key(w.ID)).MinHeight(d.ControlHeight()).Padding(d.Unit(), d.Unit()*2).Gap(d.Unit() * 2).
 		Justify(ui.Start).Radius(theme.ControlRadius).Role(ui.RoleListItem).Label(w.Name).Selected(current)
 	internal.Ring(b, k.Focus, theme.ControlRadius)
 	switch {