Iframe DOM Node Fallback

Goal

Fix Cannot resolve a Slate node from DOM node: [object HTMLParagraphElement] when clicking inside /examples/iframe.

Current Take

This is not the DOM coverage boundary feature failing. The iframe paragraph is mounted DOM, but DOMEditor.toSlateNode can lose or miss the ELEMENT_TO_NODE weak-map entry. The fallback should use Slate-owned mounted metadata (data-slate-path) only when the DOM node is inside the editor and the path still exists.

Plan

1. Reproduce the iframe click crash in the browser and capture console evidence.
2. Add a regression for toSlateNode recovering from a mounted element with data-slate-path but no weak-map entry.
3. Patch the DOM bridge fallback without accepting arbitrary foreign DOM.
4. Verify focused tests, package checks, lint, and browser click behavior.

Verification

• Done: bun test ./test/bridge.test.ts in /Users/zbeyens/git/slate-v2/packages/slate-dom.
• Done: bun --filter slate-react test:vitest -- test/rendered-dom-shape-contract.test.tsx in /Users/zbeyens/git/slate-v2.
• Done: bun --filter slate-dom typecheck.
• Done: bun --filter slate-react typecheck.
• Done: bun lint:fix.
• Done: dev-browser --connect http://127.0.0.1:9222 against http://localhost:3100/examples/iframe: iframe Slate paragraphs/text spans expose data-slate-path and clicking the first paragraph produces no page or console errors.
• Done: bun run completion-check in /Users/zbeyens/git/plate-2.
• Note: full pnpm lint:fix in /Users/zbeyens/git/plate-2 is blocked by existing benchmark/tooling diagnostics unrelated to this docs-side checkpoint; Biome ignores the touched markdown plan/solution files.