`hermes update` previously just printed a warning when it detected a
running `hermes dashboard` process from the previous version, telling
the user to kill and restart it themselves. In practice dashboards get
started and forgotten, so the warning was routinely ignored and users
ended up with a silent frontend/backend mismatch (new JS bundle served
against the old in-memory Python backend, e.g. new auth headers the old
code doesn't recognise → every API call 401s).
The dashboard has no service manager, no PID file, and we don't record
the original launch args (--host, --port, --insecure, --tui, --no-open)
so we can't auto-restart it. But we CAN stop it, which is what the
user wants — the failure mode when the stale process is left alive is
worse than the dashboard just being down.
- POSIX: SIGTERM, poll for ~3s, SIGKILL any survivors.
- Windows: `taskkill /PID <pid> /F`.
- Print each PID's outcome plus a one-line restart hint.
- Detection logic is unchanged (same ps / wmic scan, same guards
against the `pgrep -f` greedy-match trap from #16872 and the
#17049 wmic UnicodeDecodeError fix).
Also split the old monolithic `_warn_stale_dashboard_processes` into
`_find_stale_dashboard_pids` (scan) + `_kill_stale_dashboard_processes`
(kill), keeping the old name as an alias so any external callers still
work.
E2E verified: spawned a fake `hermes dashboard` cmdline via
`exec -a 'hermes dashboard …' sleep 300`, ran
`_kill_stale_dashboard_processes()`, confirmed SIGTERM exit (-15)
and that a post-scan returns an empty PID list.
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