No Docker healthchecks: the daemon keeps /metrics' counts itself (#218)

Docker runs a healthcheck with exec, and containerd puts each exec's state in XDG_RUNTIME_DIR,
/run/user/0 on Tower, which elogind removes when root's last session ends. Every check then
failed and every container showed unhealthy while all of them answered. The checks are gone from
the sample compose file and production's; ipx's library counts for /metrics, which only the
healthcheck's status call refreshed, are counted every 30 s by the daemon.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/load/run.js

@@ -8,8 +8,7 @@
 // It builds a release binary (debug Argon2 alone takes a second a sign-in, which would measure
 // the build, not ipx), serves generated feeds from this process, starts a daemon on its own
 // config and data under /tmp/ipx-load, wiped first, seeds listeners, then runs each k6 script.
-// While each runs, `ipx status` -- the Docker healthcheck -- is run every second, and the run
-// fails if any answer takes as long as the healthcheck's 5s timeout.
+// While each runs, `ipx status` is run every second, and the run fails if any answer takes 5s.
 //
 // The daemon is on SQLite unless --postgres, which puts it in IPX_TEST_DATABASE_URL, the
 // database the Rust tests use on Postgres too (ipodderx_test on the server production's is on, in