fix: detect gh-copilot deprecation and improve GitHub Models 413 errors (#10648)

Address two blocking issues when using GitHub Copilot integrations:

1. ACP mode: detect the gh-copilot CLI deprecation error from stderr
   and surface an actionable message with alternatives instead of
   hanging or showing a cryptic error.

2. GitHub Models (Azure) 413: recognize models.inference.ai.azure.com
   as a known GitHub Models URL, and print a targeted hint explaining
   the hard 8K token limit that makes this endpoint incompatible with
   Hermes' system prompt size.

agent/model_metadata.py

@@ -358,6 +358,7 @@ _URL_TO_PROVIDER: Dict[str, str] = {
     "api.deepseek.com": "deepseek",
     "api.githubcopilot.com": "copilot",
     "models.github.ai": "copilot",
+    "models.inference.ai.azure.com": "github-models",
     "api.fireworks.ai": "fireworks",
     "opencode.ai": "opencode-go",
     "api.x.ai": "xai",