GitHub Copilot billing and policy overhaul: upfront seats, lifetime chat retention

GitHub's Aug 28 changelog entry details three changes: Copilot Business/Enterprise seats switch to upfront per-seat charging at each cycle start (new signups reopen Sep 1, existing customers Oct 1; per-seat prices unchanged); the cloud agent, Chat on github.com and Mobile chat merge into one policy enabled by default with chat retention extended from 28 days to account lifetime (no earlier than Sep 28); and default code-review effort moves from Lite to Balanced on Sep 28 unless admins opt out. A Copilot in Visual Studio August update also shipped Aug 28.