feat: add list servers command

src/cli.rs

@@ -5,7 +5,8 @@ use clap::{ArgGroup, Parser};
 /// Deploy hobby projects from a local PC to a VPS over SSH.
 #[derive(Debug, Parser)]
 #[command(name = "xboctploy", version, about)]
-#[command(group = ArgGroup::new("target").required(true).args(["project", "list"]))]
+#[command(arg_required_else_help = true)]
+#[command(group = ArgGroup::new("target").required(true).args(["project", "list", "list_servers"]))]
 pub struct Cli {
     /// Project name from deploy.toml
     pub project: Option<String>,
@@ -18,4 +19,7 @@ pub struct Cli {
     /// List configured projects and exit
     #[arg(long)]
     pub list: bool,
+    /// List configured servers and exit
+    #[arg(long)]
+    pub list_servers: bool,
 }