v2.7.2a3

Pre-release for live testing on agentos-railway (agno 2.7.2a3 + agnoctl 0.1.2a3, lockstep).

Over v2.7.2a2:

• Built-in AS advertises public-client auth (token_endpoint_auth_methods_supported) in its AS metadata — connector (claude.ai / ChatGPT) DCR compatibility
• agno connect reads the OAuth signal from /info mcp.oauth instead of auth_mode
• agno connect honors exported PATs on open REST planes, fails dead-ends up front, and prints a readable connect report