Provider: add GLM (Zhipu)

[csmatar]

Summary

Add GLM (Zhipu) as a provider. Zhipu's API is OpenAI Chat Completions-compatible, so this reuses the seam from #71 — data row + pricing rows + a contract test, not a new adapter.

Blocked by #71 (the OpenAI-compatible provider seam).

Scope

• Registry entry: provider name zhipu, base_url = Zhipu's OpenAI-compatible endpoint, key from ZHIPUAI_API_KEY. Verify the current base URL and env-var name at implementation time (there are separate CN and international hosts).
• Pricing rows in dryfire/data/pricing.yaml for the GLM family (e.g. zhipu:glm-4.6).
• Offline contract test from a recorded GLM payload (one tool-call turn).
• One @pytest.mark.live smoke test behind ZHIPUAI_API_KEY.

Acceptance

• provider: zhipu runs from a recorded cassette with no adapter code beyond the seam.
• make check green, offline.

Notes

GLM is also reachable via an Anthropic-compatible endpoint on some hosts; we standardize on the OpenAI-compatible path here to reuse the seam. Flag it if tool-calling parity forces the Anthropic path instead.