swarmexec v1.16.0 — healthchecks in the tree, image cleanup per node

- The service tree is coloured by healthcheck, not only by replica count. A
  service whose every container was failing its probe used to render as a calm
  aqua "3/3": the count was true and the row was misleading. Swarm cannot tell
  you otherwise — a task reads "running" while its container fails every probe
  — so the verdict comes from the node. Every container failing is now as bad
  as none running; some failing reads like a partial rollout. A service that
  declares no healthcheck is deliberately NOT recoloured: nothing is known, and
  guessing would be the same mistake in the other direction. Stacks roll the
  same verdict up.
- "No healthcheck configured" and "the probe passes" stay different facts
  everywhere. Empty never means healthy.
- Image disk space, per node. A node whose filesystem fills with old layers was
  invisible from the cluster side — the manager API has no view of images at
  all. The node detail now shows what the layer store holds and what is
  reclaimable, and "P" reclaims it.
- The two reclaim modes are two menu entries, not one flag with a default,
  because they are different acts: untagged leftovers are safe to remove, while
  removing every unused image also takes images that services scaled to zero
  and tasks between restarts still need — each then has to pull again. The
  agent authorizes the two separately, so a policy can permit one without the
  other.
- The image figures match `docker system df` exactly. Summing image sizes does
  not: layers are shared, and that sum reported 32.7 GB where the daemon said
  22.2 GB.

Health markers and the image view both need the agents redeployed: run
`swarmexec init --force`. Until then they stay absent, and say so.