Adds GLM (Zhipu / Z.ai) as a built-in provider.
- GLM models (
glm-4.6,glm-4.5,glm-4.5-flash, …) route tohttps://api.z.ai/api/paas/v4— Zhipu's OpenAI-compatible endpoint — via the existing passthrough path. - Set
GLM_API_KEYand use aglm-*model. OverridebaseUrlfor the coding-plan (/api/coding/paas/v4) or mainland (open.bigmodel.cn) endpoints. - Works across all three inbound formats; cross-converts for
/v1/messages. - 18 tests, all passing.