Move outside links before breaking at their end

[dylans]

Pressing Enter with a collapsed caret inside the end of a link duplicated an empty link into the next paragraph. Move that caret to the following text node before the example's normal insertBreak runs.

Fixes #4334

Case	Before	After
Enter inside the end of a link	Empty link in the next paragraph	Next paragraph starts outside the link
Enter inside the middle of a link	Splits the link	Unchanged
Enter with part of the link selected	Replaces the selection and splits the link	Unchanged

Regenerate only the matching JSX. This example-only fix needs no changeset. The override targets link nodes only and delegates the actual paragraph split to the existing handler.

Validation: the link-end regression fails on main 8f59fd3 in Chromium, Firefox and WebKit; the two consequence cases pass on main. All three cases pass twice with the fix in each desktop browser (18 passed / 6 synthetic-mobile cases skipped).

check.sh passed on Node 24.21.0: 1,468 Mocha / 141 Jest tests, build, TypeScript, ESLint and Prettier. Playwright TypeScript also passes.

Full browser suite: 271 passed / 20 skipped / one Chromium Markdown list failure, also reproduced on main 8f59fd3 (2 failures / 10 passes across four Markdown-test repeats). All new link tests pass. The markdown-shortcuts failure is a test-timing flake (a click processed after the keys that follow it), fixed separately in #6205.

[changeset-bot]

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Latest commit: d91b9d5

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