Implement real-time terminal popup for system rebuild operations

- Add terminal popup UI component with 80% screen coverage and terminal styling
- Extend ZMQ protocol with CommandOutputMessage for streaming output
- Implement real-time output streaming in agent system rebuild handler
- Add keyboard controls (ESC/Q to close, ↑↓ to scroll) for popup interaction
- Fix system panel Build display to show actual NixOS build instead of config hash
- Update service filters in README with wildcard patterns for better matching
- Add periodic progress updates during nixos-rebuild execution
- Integrate command output handling in dashboard main loop

dashboard/src/communication/mod.rs

@@ -1,5 +1,5 @@
 use anyhow::Result;
-use cm_dashboard_shared::{MessageEnvelope, MessageType, MetricMessage};
+use cm_dashboard_shared::{CommandOutputMessage, MessageEnvelope, MessageType, MetricMessage};
 use tracing::{debug, error, info, warn};
 use zmq::{Context, Socket, SocketType};
 
@@ -103,6 +103,43 @@ impl ZmqConsumer {
         Ok(())
     }
 
+    /// Receive command output from any connected agent (non-blocking)  
+    pub async fn receive_command_output(&mut self) -> Result<Option<CommandOutputMessage>> {
+        match self.subscriber.recv_bytes(zmq::DONTWAIT) {
+            Ok(data) => {
+                // Deserialize envelope
+                let envelope: MessageEnvelope = serde_json::from_slice(&data)
+                    .map_err(|e| anyhow::anyhow!("Failed to deserialize envelope: {}", e))?;
+
+                // Check message type
+                match envelope.message_type {
+                    MessageType::CommandOutput => {
+                        let cmd_output = envelope
+                            .decode_command_output()
+                            .map_err(|e| anyhow::anyhow!("Failed to decode command output: {}", e))?;
+
+                        debug!(
+                            "Received command output from {}: {}",
+                            cmd_output.hostname,
+                            cmd_output.output_line
+                        );
+
+                        Ok(Some(cmd_output))
+                    }
+                    _ => Ok(None), // Not a command output message
+                }
+            }
+            Err(zmq::Error::EAGAIN) => {
+                // No message available (non-blocking mode)
+                Ok(None)
+            }
+            Err(e) => {
+                error!("ZMQ receive error: {}", e);
+                Err(anyhow::anyhow!("ZMQ receive error: {}", e))
+            }
+        }
+    }
+
     /// Receive metrics from any connected agent (non-blocking)
     pub async fn receive_metrics(&mut self) -> Result<Option<MetricMessage>> {
         match self.subscriber.recv_bytes(zmq::DONTWAIT) {
@@ -132,6 +169,10 @@ impl ZmqConsumer {
                         debug!("Received heartbeat");
                         Ok(None) // Don't return heartbeats as metrics
                     }
+                    MessageType::CommandOutput => {
+                        debug!("Received command output (will be handled by receive_command_output)");
+                        Ok(None) // Command output handled by separate method
+                    }
                     _ => {
                         debug!("Received non-metrics message: {:?}", envelope.message_type);
                         Ok(None)