Python package 0.3.8: checkout credential handoff

Python package 0.3.8: checkout credential handoff

Checkout requests now forward an available configured or per-request ParlayAPI key for backend account-ownership validation. Keyless checkout retains the email flow; its acknowledgement does not confirm delivery. Other public tools continue to omit the key.

Existing standalone tools, qualified arbitrage wording, dependencies and tool signatures are preserved. Both Python distribution formats passed the nine offline checkout tests and real SDK metadata discovery of all 22 tools. No live account, billing or email action was included in those checks.

This is a Python distribution update. The separately pinned desktop bundle remains 0.3.6 and does not include this fix. Hosted API/vendor delivery is separate.