feat(richtext-attachment): wire the shared link editor into the article editor

Replace the ad-hoc English UIAlertController link prompt in the RichText
attachment screen with `chatTextLinkEditController` from ChatTextLinkEditUI —
the same UI the chat composer uses. It reads the current selection + existing
link from the editor's native API (`selectedText()` / `currentLink()`) and
applies the result back (`setLink` / `removeLink`, empty string = remove),
gaining localized strings, the URL keyboard field, live webpage preview, and
clipboard-URL prefill.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>