Adds an `on-exit` cron schedule kind: a job fires once when a watched command/process
exits, via gateway ProcessSupervisor exit watchers. Covers CLI (`--on-exit`/`--on-exit-cwd`),
tool/protocol schema, RPC list-filter, Control UI + macOS read-only display, SQLite
round-trip, and origin-aware wake routing. Restart-safe one-shot (persists completion
before firing); platform-aware shell; bounded watched-command execution.
Squashed from 22 iterative commits for a clean rebase onto current main.
