[FEATURE]: Remove overly strict git mutation restriction in Kimi system prompt (kimi.txt)

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

PR #20259 introduced a dedicated system prompt for Kimi, but it contains a very strict restriction on git mutations:

https://github.com/anomalyco/opencode/blob/dff8fbc149fb7492e4f07b713ac31ea70d9a541c/packages/opencode/src/session/prompt/kimi.txt#L45

Because of this, the agent cannot automatically make atomic commits or other git actions when using Kimi, even if I have allowed commits in AGENTS.md.

Also, none of the other model system prompts have restriction like that.

I think this rule is unsuitable and should be removed.