Add agent version reporting and display

- Agent reports version via agent_version metric using nix store hash
- Dashboard displays agent version in system widget
- Foundation for cross-host version comparison
- Both agent -V and dashboard show versions

agent/src/main.rs

@@ -13,10 +13,26 @@ mod status;
 
 use agent::Agent;
 
+/// Get version showing cm-dashboard-agent package hash for easy deployment verification
+fn get_version() -> &'static str {
+    // Get the path of the current executable
+    let exe_path = std::env::current_exe().expect("Failed to get executable path");
+    let exe_str = exe_path.to_string_lossy();
+    
+    // Extract Nix store hash from path like /nix/store/HASH-cm-dashboard-v0.1.8/bin/cm-dashboard-agent
+    let hash_part = exe_str.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-agent")]
 #[command(about = "CM Dashboard metrics agent with individual metric collection")]
-#[command(version)]
+#[command(version = get_version())]
 struct Cli {
     /// Increase logging verbosity (-v, -vv)
     #[arg(short, long, action = clap::ArgAction::Count)]