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>

agent/memory_panel.go

@@ -30,7 +30,7 @@ type MemoryPanelOptions struct {
 
 // MemoryPanelResult reports this frame's in-place edits.
 type MemoryPanelResult struct {
-	Element *ui.Element
+	Element ui.Element
 	// Edited and Deleted are changed IDs, else "".
 	Edited  string
 	Deleted string
@@ -74,7 +74,7 @@ func MemoryPanel(c *ui.Context, entries *[]MemoryEntry, opts MemoryPanelOptions)
 		}
 		AgentRows(c, len(st.shown), func(i int) {
 			idx := st.shown[i]
-			ui.Column(c).Key((*entries)[idx].ID).Children(func() { memoryRow(c, entries, idx, st, locked, &r) })
+			ui.Column(c.Key((*entries)[idx].ID)).Children(func() { memoryRow(c, entries, idx, st, locked, &r) })
 		}).Shrink(1).MaxHeight(maxH).Dividers(theme.BorderWidth, core.Tokens(c).Border)
 	})
 	if r.Deleted != "" {
@@ -123,7 +123,7 @@ func memoryRow(c *ui.Context, entries *[]MemoryEntry, idx int, st *memoryPanelSt
 	u := core.Density(c).Unit()
 	ui.Column(c).Gap(u).Padding(u*2, 0).Children(func() {
 		if st.editing == e.ID && !locked {
-			input.TextArea(c, &st.draft, input.TextAreaOptions{Label: core.Msg(c, "memory_panel.edit"), MinHeight: 60}).Input.AutoFocus()
+			core.AutoFocus(c, input.TextArea(c, &st.draft, input.TextAreaOptions{Label: core.Msg(c, "memory_panel.edit"), MinHeight: 60}).Input)
 			ui.Row(c).Gap(u * 2).Justify(ui.End).Children(func() {
 				if input.Button(c, core.Msg(c, "memory_panel.cancel"), input.ButtonOptions{Variant: input.Secondary}).Clicked() {
 					st.editing = ""