fix: omit pinned sampling params for Moonshot Kimi K2/K3 (#1191)

Moonshot rejects temperature and top_p on Kimi K2/K3 families. Chatbox
was sending session defaults, so chat and provider connection tests failed
with invalid_request_error.

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
(cherry picked from commit 371b2e2cb713ec2043583b38f2448e9092bfb241)

(cherry picked from pro commit ae35c3299c476d5c335fb40b8b2afaf33bd0c346)