[finish] Jaah nodes Graviton AWS Ubuntu compatibility

Terminal analytical phase: verify every build subtask has completed and resolved, optionally note UI acceptance evidence, then settle. Dispatched as a read-only runner role whose settle is server-computed (`task.complete` declaring a `finish` terminal) — the server derives the full finish report and flips this child `-> done`; the runner attests nothing. Readied by the fan-out sweep like its siblings; its dependency edges to every coder keep `dispatchable_tasks` from dispatching it until those deps are done.

All 7 build children done; 10/10 supported cells green on real dev EC2, same install command. Exceptions: C-9 arm64/Windows (operator-accepted), GHA unproven (no repo). Active outside epic: 11244, 11254. Filed follow-up 11262 (node console polish). Memory: none applied.