Backfills the E4 deep-review's deferred Modal focus-management test. jsdom
returns null for every offsetParent (no layout), so focusablesIn() would see
zero controls; the test stubs HTMLElement.prototype.offsetParent to report
"visible" for connected nodes (what a real browser reports for the shown
dialog), and a second describe documents the raw-jsdom empty-guard path.
Covers: initial focus on open, Tab/Shift+Tab edge-wrap, pull-back on escaped
focus, the active===panel leak guard, no-trap in the interior, Escape closes
the topmost only, and restore-to-trigger on unmount. useBackToClose is mocked
(its history stack is covered by history.dom.test.ts).
10 tests; full FE gate green (tsc/eslint/prettier/knip, 257 vitest).
peter
fa8bdf83a8