Implement WakeOnLAN functionality with simplified configuration

- Add Status::Offline enum variant for disconnected hosts
- All configured hosts now always visible showing offline status when disconnected
- Add WakeOnLAN support using wake-on-lan Rust crate
- Implement w key binding to wake offline hosts with MAC addresses
- Simplify configuration to single [hosts] section with MAC addresses only
- Change critical status icon from ◯ to ! for better visibility
- Add proper MAC address parsing and error handling
- Silent WakeOnLAN operation with logging for success/failure

Configuration format:
[hosts]
hostname = { mac_address = "AA:BB:CC:DD:EE:FF" }

dashboard/src/app.rs

@@ -67,8 +67,8 @@ impl Dashboard {
             }
         };
 
-        // Connect to predefined hosts from configuration
-        let hosts = config.hosts.predefined_hosts.clone();
+        // Connect to configured hosts from configuration
+        let hosts: Vec<String> = config.hosts.keys().cloned().collect();
 
         // Try to connect to hosts but don't fail if none are available
         match zmq_consumer.connect_to_predefined_hosts(&hosts).await {