Add agent hash display to system panel

Implement agent version tracking to diagnose deployment issues:
- Add get_agent_hash() method to extract Nix store hash from executable path
- Collect system_agent_hash metric in NixOS collector
- Display "Agent Hash" in system panel under NixOS section
- Update metric filtering to include agent hash

This helps identify which version of the agent is actually running
when troubleshooting deployment or metric collection issues.

agent/src/collectors/nixos.rs

@@ -46,6 +46,23 @@ impl NixOSCollector {
         Ok(clean_version)
     }
 
+    /// Get agent hash from binary path
+    fn get_agent_hash(&self) -> Result<String, Box<dyn std::error::Error>> {
+        // Get the path of the current executable
+        let exe_path = std::env::current_exe()?;
+        let exe_str = exe_path.to_string_lossy();
+        
+        // Extract Nix store hash from path like /nix/store/fn804fh332mp8gz06qawminpj20xl25h-cm-dashboard-0.1.0/bin/cm-dashboard-agent
+        if let Some(store_path) = exe_str.strip_prefix("/nix/store/") {
+            if let Some(dash_pos) = store_path.find('-') {
+                return Ok(store_path[..dash_pos].to_string());
+            }
+        }
+        
+        // Fallback to "unknown" if not in Nix store
+        Ok("unknown".to_string())
+    }
+
     /// Get currently active users
     fn get_active_users(&self) -> Result<Vec<String>, Box<dyn std::error::Error>> {
         let output = Command::new("who").output()?;
@@ -131,6 +148,31 @@ impl Collector for NixOSCollector {
             }
         }
 
+        // Collect agent hash
+        match self.get_agent_hash() {
+            Ok(hash) => {
+                metrics.push(Metric {
+                    name: "system_agent_hash".to_string(),
+                    value: MetricValue::String(hash),
+                    unit: None,
+                    description: Some("Agent Nix store hash".to_string()),
+                    status: Status::Ok,
+                    timestamp,
+                });
+            }
+            Err(e) => {
+                debug!("Failed to get agent hash: {}", e);
+                metrics.push(Metric {
+                    name: "system_agent_hash".to_string(),
+                    value: MetricValue::String("unknown".to_string()),
+                    unit: None,
+                    description: Some("Agent hash (failed to detect)".to_string()),
+                    status: Status::Unknown,
+                    timestamp,
+                });
+            }
+        }
+
         debug!("Collected {} NixOS metrics", metrics.len());
         Ok(metrics)
     }

dashboard/src/ui/mod.rs

@@ -119,7 +119,7 @@ impl TuiApp {
                 // Add NixOS metrics - using exact matching for build display fix
                 let nixos_metrics: Vec<&Metric> = all_metrics
                     .iter()
-                    .filter(|m| m.name == "system_nixos_build" || m.name == "system_active_users")
+                    .filter(|m| m.name == "system_nixos_build" || m.name == "system_active_users" || m.name == "system_agent_hash")
                     .copied()
                     .collect();
                 system_metrics.extend(nixos_metrics);

dashboard/src/ui/widgets/system.rs

@@ -16,6 +16,7 @@ pub struct SystemWidget {
     // NixOS information
     nixos_build: Option<String>,
     active_users: Option<String>,
+    agent_hash: Option<String>,
     
     // CPU metrics
     cpu_load_1min: Option<f32>,
@@ -64,6 +65,7 @@ impl SystemWidget {
         Self {
             nixos_build: None,
             active_users: None,
+            agent_hash: None,
             cpu_load_1min: None,
             cpu_load_5min: None,
             cpu_load_15min: None,
@@ -313,6 +315,11 @@ impl Widget for SystemWidget {
                         self.active_users = Some(users.clone());
                     }
                 }
+                "system_agent_hash" => {
+                    if let MetricValue::String(hash) = &metric.value {
+                        self.agent_hash = Some(hash.clone());
+                    }
+                }
                 
                 // CPU metrics
                 "cpu_load_1min" => {
@@ -397,6 +404,11 @@ impl Widget for SystemWidget {
             Span::styled(format!("Active users: {}", users_text), Typography::secondary())
         ]));
 
+        let agent_hash_text = self.agent_hash.as_deref().unwrap_or("unknown");
+        lines.push(Line::from(vec![
+            Span::styled(format!("Agent Hash: {}", agent_hash_text), Typography::secondary())
+        ]));
+
         // CPU section
         lines.push(Line::from(vec![
             Span::styled("CPU:", Typography::widget_title())