feat(azure-foundry): add Microsoft Entra ID auth

Use azure-identity DefaultAzureCredential for keyless Foundry auth.

Preserve refreshable callable credentials through OpenAI and Anthropic client paths.

Add setup, doctor, auth status, docs, and tests for Entra auth.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

agent/context_compressor.py

@@ -486,7 +486,7 @@ class ContextCompressor(ContextEngine):
         model: str,
         context_length: int,
         base_url: str = "",
-        api_key: str = "",
+        api_key: Any = "",
         provider: str = "",
         api_mode: str = "",
     ) -> None: