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/ui/theme.rs

@@ -147,6 +147,7 @@ impl Theme {
             Status::Warning => Self::warning(),
             Status::Critical => Self::error(),
             Status::Unknown => Self::muted_text(),
+            Status::Offline => Self::muted_text(), // Dark gray for offline
         }
     }
 
@@ -244,8 +245,9 @@ impl StatusIcons {
             Status::Ok => "●",
             Status::Pending => "◉", // Hollow circle for pending
             Status::Warning => "◐",
-            Status::Critical => "◯",
+            Status::Critical => "!",
             Status::Unknown => "?",
+            Status::Offline => "○", // Empty circle for offline
         }
     }
 
@@ -258,6 +260,7 @@ impl StatusIcons {
             Status::Warning => Theme::warning(),    // Yellow
             Status::Critical => Theme::error(),     // Red
             Status::Unknown => Theme::muted_text(), // Gray
+            Status::Offline => Theme::muted_text(), // Dark gray for offline
         };
 
         vec![