Submit root events through the local socket

Submit root events through the local socket

One local notify command accepts a source, event ID, and text, then
prints a private accepted or duplicate receipt. It rejects unsupported
targets and fields instead of redirecting input. The receipt does not
claim that an agent has processed the event.

Caller cancellation and a submission deadline stop pending socket I/O.
The command help states the root-only test scope, input bounds, and
fixed receipt capacity. Isolated socket checks cover intake, retries,
output failures, cancellation, and receipt privacy.

Issue: 44d8703