Control remote fleet workers over SSH with user, host, and key path

NS1 is marchon@70.88.205.138 using ~/.ssh/id_ed25519. Private key
bytes stay off git. Spawn, health, and kill go through ssh; remote
workers bind loopback only.

packages/verae-fleet/machines.secrets.json.example

@@ -0,0 +1,13 @@
+{
+  "ns1": {
+    "user": "marchon",
+    "host": "70.88.205.138",
+    "sshPort": 22,
+    "identityFile": "~/.ssh/id_ed25519"
+  },
+  "lan-134": {
+    "user": "marchon",
+    "host": "70.88.205.134",
+    "identityFile": "~/.ssh/id_ed25519"
+  }
+}