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/config/mod.rs

@@ -6,7 +6,7 @@ use std::path::Path;
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct DashboardConfig {
     pub zmq: ZmqConfig,
-    pub hosts: HostsConfig,
+    pub hosts: std::collections::HashMap<String, HostDetails>,
     pub system: SystemConfig,
     pub ssh: SshConfig,
     pub service_logs: std::collections::HashMap<String, Vec<ServiceLogConfig>>,
@@ -18,10 +18,10 @@ pub struct ZmqConfig {
     pub subscriber_ports: Vec<u16>,
 }
 
-/// Hosts configuration
+/// Individual host configuration details
 #[derive(Debug, Clone, Serialize, Deserialize)]
-pub struct HostsConfig {
-    pub predefined_hosts: Vec<String>,
+pub struct HostDetails {
+    pub mac_address: Option<String>,
 }
 
 /// System configuration
@@ -68,8 +68,3 @@ impl Default for ZmqConfig {
     }
 }
 
-impl Default for HostsConfig {
-    fn default() -> Self {
-        panic!("Dashboard configuration must be loaded from file - no hardcoded defaults allowed")
-    }
-}