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/Model/API/PingService.swift

@@ -1,7 +1,10 @@
 import Foundation
+import UserNotifications
 
 enum PingService {
-    static func ping(hostname: String, apiKey: String) async -> Bool {
+    private static var previousPingStates: [String: Bool] = [:]
+
+    static func ping(hostname: String, apiKey: String, notificationsEnabled: Bool = true) async -> Bool {
         guard let url = URL(string: "https://\(hostname)/api/v2/ping") else {
             print("❌ [PingService] Invalid URL for \(hostname)")
             return false
@@ -18,17 +21,49 @@ enum PingService {
                 if let responseString = String(data: data, encoding: .utf8) {
                     print("❌ [PingService] HTTP \(httpResponse.statusCode): \(responseString)")
                 }
+                handlePingFailure(for: hostname, notificationsEnabled: notificationsEnabled)
                 return false
             }
 
             if let result = try? JSONDecoder().decode([String: String].self, from: data), result["response"] == "pong" {
+                handlePingSuccess(for: hostname, notificationsEnabled: notificationsEnabled)
                 return true
             } else {
+                handlePingFailure(for: hostname, notificationsEnabled: notificationsEnabled)
                 return false
             }
         } catch {
             print("❌ [PingService] Error pinging \(hostname): \(error)")
+            handlePingFailure(for: hostname, notificationsEnabled: notificationsEnabled)
             return false
         }
     }
+
+    private static func handlePingSuccess(for hostname: String, notificationsEnabled: Bool) {
+        let wasPreviouslyDown = previousPingStates[hostname] == false
+        previousPingStates[hostname] = true
+
+        if wasPreviouslyDown && notificationsEnabled {
+            sendNotification(title: "Server Online", body: "\(hostname) is now online")
+        }
+    }
+
+    private static func handlePingFailure(for hostname: String, notificationsEnabled: Bool) {
+        let wasPreviouslyUp = previousPingStates[hostname] != false
+        previousPingStates[hostname] = false
+
+        if wasPreviouslyUp && notificationsEnabled {
+            sendNotification(title: "Server Offline", body: "\(hostname) is offline")
+        }
+    }
+
+    private static func sendNotification(title: String, body: String) {
+        let content = UNMutableNotificationContent()
+        content.title = title
+        content.body = body
+        content.sound = .default
+
+        let request = UNNotificationRequest(identifier: UUID().uuidString, content: content, trigger: nil)
+        UNUserNotificationCenter.current().add(request)
+    }
 }