Merge PR #420: fix: respect OPENAI_BASE_URL when resolving API key priority

Authored by manuelschipper. Adds GLM-4.7 and GLM-5 context lengths (202752)
to model_metadata.py. The key priority fix (prefer OPENAI_API_KEY for
non-OpenRouter endpoints) was already applied in PR #295; merged the Z.ai
mention into the comment.

agent/model_metadata.py

@@ -49,6 +49,8 @@ DEFAULT_CONTEXT_LENGTHS = {
     "meta-llama/llama-3.3-70b-instruct": 131072,
     "deepseek/deepseek-chat-v3": 65536,
     "qwen/qwen-2.5-72b-instruct": 32768,
+    "glm-4.7": 202752,
+    "glm-5": 202752,
 }