feat: add status notifications for server monitoring

- Add notification preferences (Status Notifications and Alert Notifications toggles)
- Implement ping failure/recovery notifications when servers go offline/online
- Track individual service status changes and notify when services fail
- Request notification permissions on app launch
- Services like DNS, FTP, SSH, etc. now trigger alerts when status changes
- Notifications only sent when settings are enabled

Changes:
- PreferencesView: Add NotificationsPreferencesView with two toggles
- PingService: Add notification support with state tracking for ping events
- MainView: Add service status monitoring with change detection
- Track previous service states to detect transitions

Sources/Views/PreferencesView.swift

@@ -260,19 +260,18 @@ private struct UpdatesPreferencesView: View {
 }
 
 private struct NotificationsPreferencesView: View {
-    var body: some View {
-        VStack(alignment: .leading, spacing: 12) {
-            Text("Notifications")
-                .font(.headline)
-                .padding(.bottom)
+    @AppStorage("enableStatusNotifications") private var enableStatusNotifications: Bool = true
+    @AppStorage("enableAlertNotifications") private var enableAlertNotifications: Bool = true
 
-            Text("Configure notification behavior here.")
-                .foregroundColor(.secondary)
+    var body: some View {
+        VStack(alignment: .leading, spacing: 18) {
+            Toggle("Status Notifications", isOn: $enableStatusNotifications)
+            Toggle("Alert Notifications", isOn: $enableAlertNotifications)
 
             Spacer()
         }
+        .toggleStyle(.switch)
         .frame(maxWidth: .infinity, alignment: .leading)
-        .padding()
     }
 }