[Docs] Correct model mapping preset guidance

[roomote-community]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote, in the web UI, or in Discord.

What changed

• distinguish the provider Default model mapping from differentiated presets
• document the current OpenAI, ChatGPT subscription, and GitHub Copilot recommended coding models
• clarify that setup applies the Default preset and that admins can apply another preset later

Why this change was made

The daily public-documentation audit reviewed all 6 first-parent commits merged to develop during the exact window from 2026-09-26T03:00:45.932Z through 2026-09-27T03:00:45.932Z. The restored model mappings in #3249 made the existing public guidance inaccurate; merged PR #3245 is already shipped, while recent open docs-audit PRs remain unshipped and do not provide the current correction.

Impact

Public model setup and mapping guidance now matches shipped behavior. This is a documentation-only change. The repository-prescribed Mintlify validation and broken-link checks passed; no screenshot is included because the local Mintlify preview retained its Compiling... development overlay after rendering the corrected page.

[roomote-community]

No code issues found. See task

_{Reviewed 77aecc3}