Decommissioning a worker from the dashboard (or swarm controller) now
asks the agent to wipe its own install before the master forgets it.
The agent stops decky containers + every decnet-* systemd unit, then
deletes /opt/decnet*, /etc/systemd/system/decnet-*, /var/lib/decnet/*,
and /usr/local/bin/decnet*. Logs under /var/log are preserved.
The reaper runs as a detached /tmp script (start_new_session=True) so
it survives the agent process being killed. Self-destruct dispatch is
best-effort — a dead worker doesn't block master-side cleanup.
Splits the three grouped router files into eight api_<verb>_<resource>.py
modules under decnet/web/router/swarm/ to match the convention used by
router/fleet/ and router/config/. Shared request/response models live in
_schemas.py. Keeps each endpoint easy to locate and modify without
stepping on siblings.
