docs: GPT-6 Sol and Luna Are Now in Teable

[Jocky-Teable]

Adds the September 24, 2026 announcement, “GPT-6 Sol and Luna Are Now in Teable,” in all 11 supported languages. The supplied cover appears directly below the title, followed by the approved three paragraphs and emphasis. Updates the localized help-center banners to the new entry.

Also fills five missing Chinese bullets in the May 28, July 26, and August 7 changelogs. Other existing entries and non-banner configuration are preserved. Based on freshly fetched main at 235f3e4.

Validation: all 11 entries compile as MDX; verified historical preservation, body text, cover placement, and banner links. Browser checks passed for every locale and LAN mobile previews. git diff --check passes.

Local preview: http://localhost:3490/en/changelog#sep-24-2026
Chinese preview: http://localhost:3490/zh/changelog#2026-09-24

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}