Separate Hide/Restore from Close for the embedded Browser: a minimized
zone keeps its body mounted (PaneBody retains the last visible viewport,
visibility:hidden + inert) instead of unmounting the <webview>, url/html
preview tiles opt into lifecycleKeepAlive via PaneMirror, the collapse
action reads "Hide" for keep-alive panes, commandFocusedPreview ignores a
hidden guest with stale native focus, and drive_preview's focus() no
longer steals the host composer while the pane is hidden.
Salvage-TRIM of #114251 (kernel only). Dropped from the original:
DESIGN.md, the apps/desktop/scripts/browser-hide-restore/ Electron smoke
harness, the three-layer host-focus bounce around executeJavaScript /
sendInputEvent / focusin in preview-pane.tsx, and the extra test files
(pane-body.test.tsx, preview-script-runner.test.ts, preview-tile.test.ts,
two of three tree-group cases).
73d4a4e9cb