feat(clan): re-enable dm-pull-deploy via forked clan-community 🌊

Stage 4e, take 2. Point the clan-community input at our fork's branch
that sanitizes machine.name for data-mesher's file-name validator
(upstream PR: clan/clan-community#25). Revisit this pin once merged.

- flake.nix: clan-community.url → fork + fix branch
- flake-modules/clan.nix: re-adds meta.domain = "clan",
  inventory.instances.data-mesher (sunken-ship bootstrap, both default),
  inventory.instances.dm-pull-deploy (sunken-ship push, both default
  action="switch"), and clanHostsModule that puts /etc/hosts entries
  for <host>.clan → each machine's ZT IPv6 so libp2p multiaddr
  resolution works without a clan-domain DNS server.
- Generator vars for data-mesher + dm-pull-deploy signing keys were
  regenerated on sunken-ship (data-mesher isn't packaged for
  aarch64-darwin, so clan vars generate runs on Linux).

vars/shared/dm-pull-deploy-signing-key/signing.key/users/danny

@@ -0,0 +1 @@
+../../../../../sops/users/danny