Follow-up to the plumbing removal: docs/swarm/README.md gets the
biggest rewrite (drops the whole "Fingerprint format" section, fixes
the runtime-effects list, the WireGuard config example + "what the
mesh does" bullet), docs/gateway.md and hive-gateway/options.nix drop
4 "needs no certFingerprint" mentions, swarm-peers-removed.nix's
migration-warning text no longer tells an upgrading operator to carry
a field over that no longer exists, swarm.nix/swarm-wireguard.nix/
swarm-controller.nix/swarm-controller's main.rs get comment fixes
where they described the now-removed HYPERHIVE_PEERS shape. Also
caught one more stale "peer hives" mention in docs/web-ui/README.md's
SW4RM tab description that the first pass on this issue missed.
c67100588e