Slate v2 Multi-root Root Chrome Focus And Padding Carets

Goal

Fix the multi-root document path where header text click, body text click, then footer text click leaves focus and native selection in the body until a second footer click.

Also fix the follow-up path where a stale body caret is restored after clicking body editor padding from another root instead of moving to the clicked body end.

Evidence

• One-off Playwright repro against http://localhost:3100/examples/multi-root-document: after scrolling the footer into view and clicking its text, active element and selection stayed in #multi-root-main.
• The same footer click works on the second attempt.
• Regression added in .tmp/slate-v2/playwright/integration/examples/multi-root-document.test.ts first failed on expect(footer).toBeFocused().
• The focused row now passes after root chrome adds a native-descendant mouseup recovery that only fires when browser focus stayed on the previous root.
• A second regression first failed with body padding keeping offset 28 from an earlier body click instead of moving to the last body paragraph end.
• The padding row now passes after direct editable-root clicks resolve the event coordinate range before falling back to selection restore.

Plan

1. Add a browser regression using real text-surface clicks, not label helpers.
2. Confirm the row fails before changing code.
3. Keep native text clicks browser-owned when they work.
4. Add a fallback for native editable descendant clicks that fail to move DOM focus after scroll.
5. Make editable-root padding clicks range-first and restore-only as fallback.
6. Verify focused Playwright, root-chrome unit tests, typecheck, lint, and completion-check.

Changeset

Package code under slate-react changes, so keep the existing branch changeset current.