Adds typed JSON build records under data/builds/<app>/<build-id>.{json,log} keyed on a stable base36 ULID-style DOKKU_BUILD_ID generated for every deploy. The new commands surface that history (builds:list, builds:info, builds:prune) and an operator-configurable retention via builds:set retention. The existing builds:cancel and builds:output now key on the build-id (with safe handling for already-finalized and abandoned records), and the per-build log file replaces journalctl as the durable source of truth for builds:output.
The DOKKU_PID now never gets overwritten except in the case that DOKKU is executed by the sudo user. If the command ends up executing a deploy, then the pid of the `dokku` owned process - which may have been executed via sudo - will be written to the file lock, allowing future commands to interact with the original process.
Additionally, the new builds plugin can be used to handle killing a build.
