fix: Use correct 'zai/' prefix for Zhipu AI models in LiteLLM

LiteLLM expects the 'zai/' provider prefix for Zhipu AI (Z.ai) models,
not 'zhipu/'. This was causing 'LLM Provider NOT provided' errors when
users configured models like 'glm-4.7' without an explicit prefix.

According to LiteLLM docs, the correct format is:
- model='zai/glm-4.7' (correct)
- NOT model='zhipu/glm-4.7' (incorrect)

This fix ensures auto-prefixed models use the correct 'zai/' format.

Fixes: Error when using Zhipu AI models with shorthand names like 'glm-4.7'

nanobot/providers/litellm_provider.py

@@ -86,13 +86,13 @@ class LiteLLMProvider(LLMProvider):
             model = f"openrouter/{model}"
         
         # For Zhipu/Z.ai, ensure prefix is present
-        # Handle cases like "glm-4.7-flash" -> "zhipu/glm-4.7-flash"
+        # Handle cases like "glm-4.7-flash" -> "zai/glm-4.7-flash"
         if ("glm" in model.lower() or "zhipu" in model.lower()) and not (
             model.startswith("zhipu/") or 
             model.startswith("zai/") or 
             model.startswith("openrouter/")
         ):
-            model = f"zhipu/{model}"
+            model = f"zai/{model}"
         
         # For vLLM, use hosted_vllm/ prefix per LiteLLM docs
         # Convert openai/ prefix to hosted_vllm/ if user specified it