docs: add note about MAX subscription not being supported

Author: root

README.md

@@ -4,6 +4,8 @@
 
 Intelligent AI model routing that cuts costs by 50-80% while maintaining quality.
 
+> **Note:** Designed for standard API key users (`ANTHROPIC_API_KEY`, `OPENAI_API_KEY`). MAX subscription OAuth is not currently supported — MAX users should continue using their provider directly.
+
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