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>

code/breakpoint_list.go

@@ -31,7 +31,7 @@ type BreakpointListOptions struct {
 
 // BreakpointListResult fields hold breakpoint IDs.
 type BreakpointListResult struct {
-	Element                 *ui.Element
+	Element                 ui.Element
 	Toggled, Edited, Opened string
 }
 
@@ -67,7 +67,7 @@ func BreakpointList(c *ui.Context, bps *[]Breakpoint, opts BreakpointListOptions
 		layout.ScrollArea(c, nil, layout.ScrollAreaOptions{}, func() {
 			for i := range *bps {
 				b := &(*bps)[i]
-				ui.Column(c).Key(b.ID).Padding(u, u*2).Gap(u).BorderWidth(0, 0, theme.BorderWidth, 0).BorderColor(k.Border).Children(func() {
+				ui.Column(c.Key(b.ID)).Padding(u, u*2).Gap(u).BorderWidth(0, 0, theme.BorderWidth, 0).BorderColor(k.Border).Children(func() {
 					ui.Row(c).MinHeight(d.ControlHeight()).Gap(u * 2).AlignItems(ui.Center).Children(func() {
 						on := b.Enabled
 						input.Checkbox(c, &on, "", input.CheckboxOptions{Disabled: opts.Disabled}).Label(fmt.Sprintf(core.Msg(c, "breakpoint_list.enable"), path.Base(b.File), b.Line))
@@ -86,7 +86,7 @@ func BreakpointList(c *ui.Context, bps *[]Breakpoint, opts BreakpointListOptions
 					switch {
 					case edit.id == b.ID:
 						in := input.TextInput(c, &edit.draft, input.TextInputOptions{Placeholder: core.Msg(c, "breakpoint_list.placeholder"), Label: core.Msg(c, "breakpoint_list.condition")})
-						in.Input.AutoFocus()
+						core.AutoFocus(c, in.Input)
 						if in.Input.Shortcut(0, ui.KeyEscape) {
 							edit.id = ""
 						} else if in.Submitted() && !disabled {
@@ -104,7 +104,7 @@ func BreakpointList(c *ui.Context, bps *[]Breakpoint, opts BreakpointListOptions
 }
 
 // breakpointLocation is a button opening the location.
-func breakpointLocation(c *ui.Context, b Breakpoint) *ui.Element {
+func breakpointLocation(c *ui.Context, b Breakpoint) ui.Element {
 	k := core.Tokens(c)
 	d := core.Density(c)
 	e := ui.ButtonBase(c).Grow(1).MinWidth(0).MinHeight(theme.MinHitSize).Justify(ui.Start).Gap(d.Unit()*2).Padding(0, d.Unit()).