Make dashboard -V show actual config hash for rebuild verification

Replace hardcoded version with first 8 characters of current system's
nix store hash. This makes it easy to verify when rebuilds complete
as the hash changes with each deployment.

No fallback - fails hard if config hash cannot be determined.

dashboard/src/main.rs

@@ -11,10 +11,31 @@ mod ui;
 
 use app::Dashboard;
 
+/// Get version showing current system config hash for easy rebuild verification
+fn get_version() -> &'static str {
+    use std::process::Command;
+    
+    // Get config hash from current system
+    let output = Command::new("readlink").arg("/run/current-system").output().expect("Failed to run readlink");
+    assert!(output.status.success(), "readlink command failed");
+    
+    let store_path = String::from_utf8_lossy(&output.stdout);
+    let store_path = store_path.trim();
+    
+    // Extract hash from nix store path
+    let hash_part = store_path.strip_prefix("/nix/store/").expect("Not a nix store path");
+    let hash = hash_part.split('-').next().expect("Invalid nix store path format");
+    assert!(hash.len() >= 8, "Hash too short");
+    
+    // Return first 8 characters of nix store hash
+    let short_hash = hash[..8].to_string();
+    Box::leak(short_hash.into_boxed_str())
+}
+
 #[derive(Parser)]
 #[command(name = "cm-dashboard")]
 #[command(about = "CM Dashboard TUI with individual metric consumption")]
-#[command(version)]
+#[command(version = get_version())]
 struct Cli {
     /// Increase logging verbosity (-v, -vv)
     #[arg(short, long, action = clap::ArgAction::Count)]