Upgrade MyGo to v0.5.5

Elements are now pass-scoped value handles: tests that read bounds
after a frame bind a ui.Handle. pixel tells frames apart by the build
pass's root, since the Tester clock no longer moves on its own.

Fix the regressions the upgrade brought:
- Clipboard reads in input handlers go through c.Services().
- MyGo notes an overlay's opener after building it, so AutoFocus
  inside lost it; pixel.AutoFocus focuses through a Handle, and
  archtest bans the raw call. Dialogs hand the focus back again.
- Elements around a press stay hovered: Tooltip tells a press-given
  focus by focus arriving under the pointer.
- The web host moves the Tester clock with real time, at most 500 ms
  a call, and gives components the real clock.

The gallery's source index also accepts CRLF checkouts.

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

files/filepreview.go

@@ -24,7 +24,7 @@ type FilePreviewOptions struct {
 type previewKey struct{}
 
 // FilePreview shows a picture, else text, in a sunken pane.
-func FilePreview(c *ui.Context, name string, pv Preview, o FilePreviewOptions) *ui.Element {
+func FilePreview(c *ui.Context, name string, pv Preview, o FilePreviewOptions) ui.Element {
 	k := pixel.K(c)
 	w, h := pixel.Or("FilePreview W", o.W, 160), pixel.Or("FilePreview H", o.H, 120)
 	return ui.Column(c).Gap(k.D(2)).AlignItems(ui.Start).Role(ui.RoleGroup).Label(name).Children(func() {