Add refresh shortkey 'r' for on-demand metrics refresh

Implements ZMQ command protocol for dashboard-to-agent communication:
- Agents listen on port 6131 for REQ/REP commands
- Dashboard sends "refresh" command when 'r' key is pressed
- Agents force immediate collection of all metrics via force_refresh_all()
- Fresh data is broadcast immediately to dashboard
- Updated help text to show "r: Refresh all metrics"

Also includes metric-level caching architecture foundation for future
granular control over individual metric update frequencies.

dashboard/src/app.rs

@@ -69,6 +69,7 @@ pub struct App {
     active_host_index: usize,
     show_help: bool,
     should_quit: bool,
+    refresh_requested: bool,
     last_tick: Instant,
     tick_count: u64,
     status: String,
@@ -106,6 +107,7 @@ impl App {
             active_host_index: 0,
             show_help: false,
             should_quit: false,
+            refresh_requested: false,
             last_tick: Instant::now(),
             tick_count: 0,
             status,
@@ -138,7 +140,8 @@ impl App {
                 self.status = "Exiting…".to_string();
             }
             KeyCode::Char('r') | KeyCode::Char('R') => {
-                self.status = "Manual refresh requested".to_string();
+                self.refresh_requested = true;
+                self.status = "Refresh requested - sending commands to agents...".to_string();
             }
             KeyCode::Left | KeyCode::Char('h') => {
                 self.select_previous_host();
@@ -156,6 +159,15 @@ impl App {
     pub fn should_quit(&self) -> bool {
         self.should_quit
     }
+    
+    pub fn check_refresh_request(&mut self) -> bool {
+        if self.refresh_requested {
+            self.refresh_requested = false;
+            true
+        } else {
+            false
+        }
+    }
 
     #[allow(dead_code)]
     pub fn status_text(&self) -> &str {
@@ -256,6 +268,10 @@ impl App {
             self.zmq_subscription.clone(),
         ))
     }
+    
+    pub fn zmq_endpoints(&self) -> &[String] {
+        &self.zmq_endpoints
+    }
 
     pub fn handle_app_event(&mut self, event: AppEvent) {
         match event {
@@ -337,6 +353,10 @@ impl App {
 
                 self.status = format!("Fetch failed • host: {} • {}", host, error);
             }
+            AppEvent::RefreshRequested => {
+                // Handle refresh command - will be implemented in the main loop
+                self.status = "Refresh command sent to all agents".to_string();
+            }
         }
     }
 
@@ -641,5 +661,6 @@ pub enum AppEvent {
         error: String,
         timestamp: DateTime<Utc>,
     },
+    RefreshRequested,
     Shutdown,
 }

dashboard/src/main.rs

@@ -153,6 +153,12 @@ fn run_app(
 
     while !app.should_quit() {
         drain_app_events(app, event_rx);
+        
+        // Check for refresh requests
+        if app.check_refresh_request() {
+            send_refresh_commands(app)?;
+        }
+        
         terminal.draw(|frame| ui::render(frame, app))?;
 
         if event::poll(tick_rate)? {
@@ -301,6 +307,58 @@ fn metrics_blocking_loop(
     Ok(())
 }
 
+fn send_refresh_commands(app: &mut App) -> Result<()> {
+    let endpoints = app.zmq_endpoints();
+    if endpoints.is_empty() {
+        return Ok(());
+    }
+    
+    let zmq_context = NativeZmqContext::new();
+    
+    for endpoint in endpoints {
+        // Convert metrics endpoint (6130) to command endpoint (6131)
+        let command_endpoint = endpoint.replace(":6130", ":6131");
+        
+        let socket = zmq_context.socket(zmq::REQ)?;
+        socket.set_linger(0)?;
+        socket.set_rcvtimeo(5000)?; // 5 second timeout
+        socket.set_sndtimeo(5000)?; // 5 second timeout
+        
+        match socket.connect(&command_endpoint) {
+            Ok(()) => {
+                debug!("Sending refresh command to {}", command_endpoint);
+                
+                match socket.send("refresh", 0) {
+                    Ok(()) => {
+                        // Wait for response
+                        match socket.recv_string(0) {
+                            Ok(Ok(response)) => {
+                                debug!("Refresh response from {}: {}", command_endpoint, response);
+                                // Update status via public method would be needed, for now just log
+                                debug!("Refresh sent to agents - response: {}", response);
+                            }
+                            Ok(Err(e)) => {
+                                warn!("String conversion error from {}: {:?}", command_endpoint, e);
+                            }
+                            Err(e) => {
+                                warn!("No response from {}: {}", command_endpoint, e);
+                            }
+                        }
+                    }
+                    Err(e) => {
+                        warn!("Failed to send refresh to {}: {}", command_endpoint, e);
+                    }
+                }
+            }
+            Err(e) => {
+                warn!("Failed to connect to command endpoint {}: {}", command_endpoint, e);
+            }
+        }
+    }
+    
+    Ok(())
+}
+
 fn handle_zmq_message(
     message: &NativeZmqMessage,
     sender: &UnboundedSender<AppEvent>,

dashboard/src/ui/dashboard.rs

@@ -80,7 +80,7 @@ fn render_help(frame: &mut Frame, area: Rect) {
     let lines = vec![
         Line::from("Keyboard Shortcuts"),
         Line::from("←/→ or h/l: Switch active host"),
-        Line::from("r: Manual refresh status"),
+        Line::from("r: Refresh all metrics"),
         Line::from("?: Toggle this help"),
         Line::from("q / Esc: Quit dashboard"),
     ];