K3 only recognizes low/high/max. Previously the Kimi provider only
forwarded low/medium/high verbatim and dropped every other level
(xhigh/max/ultra/minimal) to the thinking toggle, silently ignoring
the user's requested effort.
Now maps the full Hermes vocabulary onto K3's set, matching K3's own
server-side mapping:
low, minimal → low
medium, high → high
xhigh, max, ultra → max
ref: https://www.kimi.com/code/docs/en/kimi-code/models.html
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