feat(clan): data-mesher + dm-pull-deploy wiring 🌊

Stage 4e-a of the clan migration. Set up signed-file gossip
(data-mesher, experimental, clan-core) and pull-based NixOS deploy
(dm-pull-deploy, experimental, clan-community) across both servers.

- sunken-ship is the data-mesher bootstrap node + dm-pull-deploy push
  role; phantom-ship joins via /dns/sunken-ship.clan/tcp/7946/... — the
  hostname resolves via /etc/hosts (clanHostsModule) to sunken-ship's
  ZT IPv6 since we don't run a DNS server for the clan domain.
- Both machines run the dm-pull-deploy default role with
  action="switch": they watch /var/lib/data-mesher/files/home/
  dm_pull_deploy/target and nixos-rebuild switch against the pushed
  git+…?rev=…&narHash=… flake ref on each change.
- Signing keys (shared + per-host status) generated via clan vars
  generate, ran on sunken-ship because data-mesher isn't packaged for
  aarch64-darwin.

The legacy dotfiles-rebuild timer stays installed as a fallback until
dm-pull-deploy is proven; a smart push timer on sunken-ship (calls
dm-send-deploy only when origin/main moves) comes next.

vars/per-machine/sunken-ship/data-mesher-node-identity/identity.key/secret

@@ -0,0 +1,18 @@
+{
+	"data": "ENC[AES256_GCM,data:AlD+xw5DFrH8VwsNXqRgX/bdU2+bD1BbMSNMl+h6MloEFgMWGBt0kypqpq3LXj/p9Vtqr7rCy9N4wNAazWpQHGpA3Dv3Oka0S9xK6ghWJJWqDy1NiKkQR6a459jO7GiOzF5EGAfSp5fa4EDk/0LkIE/jkhg1ckg=,iv:+1Nsq644xQaXRIFMGfa6hv/T68YaVdNG7Aj/clKJy/o=,tag:YPpAcKkoxc6PRYxCJDcm/Q==,type:str]",
+	"sops": {
+		"age": [
+			{
+				"recipient": "age1g6y8gvcampqj5y3yzdajke2h5n7k6ckdg6a424cghy5325px7cmqjmmd28",
+				"enc": "-----BEGIN AGE ENCRYPTED FILE-----\nYWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSBmVE15YnlYcFdQSnlxYWpi\nNmtHQ3JlZmltOHBRaC9iRlpUVDRiY0NHUGxzCjhrVU9jT29vRlFmeWJTNCt3VjR0\nVHFLNUVRS0k4eExrSHRPYmlZRHZkWncKLS0tIEFQSnUwWUxzbzY0TFREaWlPdUti\nVW1GTWpoVUxwdE9VT0h1Mm8wQ2JhaFEKkfS+cJVZ3aKJi+N4N76yilDJqutMLBKZ\nfaSHFyGwOkk9kS6pf53g6GHKmakJJa9KMVGF+d2FFLgnX0XX0H9qig==\n-----END AGE ENCRYPTED FILE-----\n"
+			},
+			{
+				"recipient": "age1zy3q73pujauyajgfqwu0pnyy8732lzwvw87tu7p2xg3xuzaujc2qh6ql77",
+				"enc": "-----BEGIN AGE ENCRYPTED FILE-----\nYWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IFgyNTUxOSAzQVlkR080UmhuVHg0RlFP\nQ3phcisvY00zNTJZUFdLWUJ0ekZWRXFVRkNFCjdUc0U5ZEx3aU5ET2pIdkJzK050\nTEMzMlF4Zm9KNWR1RWY5TXBVZi9saWcKLS0tIDBHZWJWQUxoUU5BRkYvL1l0elV4\ndi90SWdkRDc1akV3ZGdiOHBhc3ppTXcKKs7RUx4WTNdEOL0J0aMZiiUD4xpnJQFC\n+Vj/6GQJmeenB1znvWZbgMUKDRhufzzg1gd8oDbjfaI1H6UP1MilNw==\n-----END AGE ENCRYPTED FILE-----\n"
+			}
+		],
+		"lastmodified": "2026-04-20T09:37:04Z",
+		"mac": "ENC[AES256_GCM,data:44xy2P1es6SKe4s2aUo1MpwSlRH262TEp+TTRpOyB0ANAunJI5ViN0Db2aHaqq0aPSiYkquIvKeqzzX9pHYqZX9Dmr37PEvoCILP5wbarO5XRCc2N53vuarEfH6xyNQCoGNw2aujpqm5ero1jJbDkYlMu2dmrAtm7y4mazcjM7s=,iv:iGzaXP7DrsEXoyntt0e/f8/M998QG9hN1Vx4C92cshU=,tag:SDm2jnXPy/gN5woNWMRcPA==,type:str]",
+		"version": "3.12.2"
+	}
+}