DOC-3526: Chat can now update an empty document

[kemister85]

Ticket: DOC-3526 (TINY-14393) TINYMCE-14393

Site: Staging

Changes:

• Add an 8.7.0 TinyMCE AI bug fix release note: the editor now sends an empty paragraph to the model when the content is empty, so Chat prompts can apply changes directly to an empty document.

Pre-checks:

• Branch is correctly prefixed: feature/8.7.0/DOC-3526_TINY-14393
• Files have been included where required (if applicable).
• Build passes without console errors, warnings, or issues.

Review:

• Documentation Team Lead has reviewed.

[kimwoodfield]

Suggested change

	In {productname} {release-version}, Chat handles an empty document the same way as the Review sidebar. When the editor is empty, Chat now inserts the generated content directly into the document instead of displaying it only in the Chat sidebar.
	In {productname} {release-version}, AI Chat can now handle updating an empty document. When the editor is empty, the generated content is now directly inserted into the document rather than only being displayed in the sidebar.