[finish] Build NodeVault Credential Encryption Feature

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 (feat/finish-as-runner, ADR-0040) whose settle is server-computed (`task.settle` 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 14 NodeVault coders done, 15 PRs merged, dev deploy green; code matches the ask. Gap: dev E2E (AC-10.1/5.7/1.3) never run — no runner reaches dev.jaah.ai — filed as Task 5480.