[Docs] Correct judgment model guidance grammar

[roomote-community]

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

What changed

• rewrite the judgment-model documentation bullet as a complete sentence that clearly explains the advisory diff-risk ranking
• clarify that the diff-risk tool returns a result with available: false when no hosted judgment model is configured

Why this change was made

Both recently added descriptions contained malformed prose that obscured the intended behavior. The corrections keep the existing judgment-model and tool contracts unchanged.

Impact

Public documentation and developer-facing tool guidance now describe the diff-risk pre-screen clearly. There is no runtime behavior change.

Screenshots

Representative rendering on the configured local docs origin. The Mintlify preview returned an internal server error after hot reload, so this demonstrates the corrected copy's readability rather than the real preview runtime.

[roomote-community]

No code issues found. See task

_{Reviewed 398a4ba}