feat: expand discovery with systemd services, LXC/VMs, SSH terminal, and filebrowser

- Add systemd service discovery to backend
- Add Proxmox LXC/VM detection
- Add hostType field to config for better host categorization
- Fix SSH trust between hosts (ubuntu/grizzley -> truenas/proxmox)
- Add SSH terminal support via xterm.js
- Add filebrowser for browsing host filesystems
- Update frontend types and components for new node types

server/hosts.json

@@ -0,0 +1,56 @@
+{
+  "hosts": [
+    {
+      "name": "ubuntu",
+      "ip": "192.168.50.61",
+      "sshUser": "bear",
+      "sshKeyPath": "~/.ssh/id_ed25519",
+      "sshPort": 22,
+      "hostType": "docker-host"
+    },
+    {
+      "name": "grizzley",
+      "ip": "192.168.50.84",
+      "sshUser": "bear",
+      "sshKeyPath": "~/.ssh/id_ed25519",
+      "sshPort": 22,
+      "hostType": "docker-host"
+    },
+    {
+      "name": "truenas",
+      "ip": "192.168.50.12",
+      "sshUser": "root",
+      "sshKeyPath": "~/.ssh/id_ed25519",
+      "sshPort": 22,
+      "hostType": "truenas"
+    },
+    {
+      "name": "proxmox",
+      "ip": "192.168.50.11",
+      "sshUser": "root",
+      "sshKeyPath": "~/.ssh/id_ed25519",
+      "sshPort": 22,
+      "hostType": "proxmox"
+    },
+    {
+      "name": "ice",
+      "ip": "192.168.50.197",
+      "sshUser": "bear",
+      "sshKeyPath": "~/.ssh/id_ed25519",
+      "sshPort": 22,
+      "hostType": "docker-host"
+    },
+    {
+      "name": "panda",
+      "ip": "192.168.50.196",
+      "sshUser": "bear",
+      "sshKeyPath": "~/.ssh/id_ed25519",
+      "sshPort": 22,
+      "hostType": "docker-host"
+    }
+  ]
+}
+  ]
+}
+  ]
+}