feat: add kimi-k2:free model

[nick-galluzzo]

This PR adds the model definition for moonshotai/kimi-k2:free for OpenRouter. It was also mentioned in: anomalyco/opencode#1002.

[wienans]

The problem with free models is that they not always support tool calls. Not all providers support them, see here: https://openrouter.ai/moonshotai/kimi-k2:free

additionally there are already pull requests for the free qwen coder and kimi k2.
I am not sure but I think they might not extend with more free models, as they are deprecated more often and updating the library is even more effort with all the free models.

[nick-galluzzo]

@wienans Thanks for the feedback.

You mentioned tool use support. I might be looking in the wrong place, but the link you provided seems to indicate that tool use is supported for kimi-k2:free. I also confirmed this by filtering on the OpenRouter models page here: https://openrouter.ai/models?q=kimi%20k2&fmt=cards&supported_parameters=tools

I also tested this with the configuration in my PR and can confirm that tool calls are working as expected.

I understand the concern about maintenance overhead for free models. Do you know how frequently they tend to be deprecated? I believe adding the popular free-tier models is beneficial for the project as it lowers the barrier for new users (and users who stick to the free tiers) to start experimenting with the library.

Let me know your thoughts! Happy to close my PR due to the other kimi k2 PR.

[wienans]

My concern was the provider specific options. The second provider (of 2) doesn’t have tool use enabled as far as I can see.

But at the end all our discussion doesn’t mean anything the decisions is on the maintainers. I am aligned with you that it would be beneficial with popular free models, and I don’t know how long providers provide them.

[fwang]

Appreciate the discussion @nick-galluzzo @wienans!

Let's add the free models for now as it is beneficial the users. And with the help of the community, we'll keep it updated once they are deprecated.

[fwang]

Btw, in opencode, you can specify which provider for OpenRouter to route to. This is an example w/ Qwen3 coder

    "openrouter": {
      "models": {
        "qwen/qwen3-coder": {
          "name": "Qwen3 Coder (DeepInfra)",
          "options": {
            "provider": {
              "order": ["deepinfra/fp8"],
              "allow_fallbacks": false
            }
          }
        }
      }
    },