PraisonAI call server exposes unauthenticated agent listing, invocation, and deletion when CALL_SERVER_TOKEN is unset

PraisonAI is a multi-agent teams system. Prior to version 4.6.40, PraisonAI's call server exposes a network-facing agent control API without authentication when `CALL_SERVER_TOKEN` is not configured. The affected component is the `praisonai.api.agent_invoke` router as mounted by `praisonai.api.call`. The authentication helper `verify_token()` fails open when `CALL_SERVER_TOKEN` is unset. Since every sensitive agent-control endpoint depends on this helper, starting the call server without a token allows any reachable client to list agents, inspect agent metadata and instructions, invoke agents, and unregister agents. This is security-relevant because the bundled call server includes the vulnerable router and binds to `0.0.0.0`. As a result, operators who launch the call server without explicitly setting `CALL_SERVER_TOKEN` may unintentionally expose an unauthenticated remote agent control plane. Version 4.6.40 fixes the issue.