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>

navigation/command_palette.go

@@ -33,7 +33,7 @@ type CommandPaletteOptions struct {
 
 // CommandPaletteResult is the built CommandPalette; Element is nil while closed.
 type CommandPaletteResult struct {
-	Element *ui.Element
+	Element ui.Element
 	chosen  string
 }
 
@@ -79,7 +79,7 @@ func CommandPalette(c *ui.Context, open *bool, commands []Command, opts CommandP
 	k := core.Tokens(c)
 	d := core.Density(c)
 	u := d.Unit()
-	res.Element = ui.DialogBase(c, open, func(back, panel *ui.Element) {
+	res.Element = ui.DialogBase(c, open, func(back, panel ui.Element) {
 		ww, wh := c.Size()
 		p := core.OverlayEnter(c, panel)
 		back.Background(ui.RGBA(0, 0, 0, 0.4*p)).Justify(ui.Start)
@@ -87,10 +87,10 @@ func CommandPalette(c *ui.Context, open *bool, commands []Command, opts CommandP
 		panel.Margin(wh*0.12, 0, 0, 0).Width(560).MaxWidth(ww - 32).MaxHeight(wh * 0.76).
 			AlignItems(ui.Stretch).Label(core.Msg(c, "command_palette.label"))
 		found := commandPaletteFilter(commands, st.query)
-		var in *ui.Element
+		var in ui.Element
 		ui.Row(c).AlignItems(ui.Center).Gap(u*3).Padding(u*3, u*4).Children(func() {
 			ui.Icon(c, icons.Must("search")).Size(16, 16).TextColor(k.TextMuted)
-			in = ui.TextInputBase(c, &st.query).FillWidth().AutoFocus().Label(core.Msg(c, "command_palette.search"))
+			in = core.AutoFocus(c, ui.TextInputBase(c, &st.query).FillWidth()).Label(core.Msg(c, "command_palette.search"))
 		})
 		ui.Box(c).Height(1).Background(k.Ornament).Role(ui.RoleNone)
 		if in.Changed() {