Product Update: success-gated Autonomous Engineering Task billing

Autonomous Engineering Task billing is now fully success-gated at the database level: two separate functions handle marking a run "completed" (which requires a real PR and an updated ticket) versus "terminal" (failed, cancelled, or retry-limit-reached) — deliberately two functions rather than one with a client-settable flag, so no client call can ever mark a run both terminal and billable at once.

Completion deliberately never requires a deploy to have happened — only a real PR and a real ticket update — closing a loophole where teams that gate their own deploys separately would otherwise never get billed for genuinely completed engineering work.

Autonomous Engineering Tasks now run on a prepaid Ticket Balance (any amount, $30 minimum) rather than a monthly allowance, billed per ticket at a volume-tiered rate — $5.00 down to $3.00 depending on cumulative ticket count — instead of a flat per-credit price. Balance never expires, and balance, purchase history, and usage history are all visible in-app with full CSV export.