feat(healthchat): ring calls via gateway VoIP push

CallKit rejects the NSE hand-off without the filtering entitlement.

ElementX/Sources/Application/Settings/AppSettings.swift

@@ -30,6 +30,10 @@ nonisolated protocol CommonSettingsProtocol: AnyObject, Sendable {
     var enableOnlySignedDeviceIsolationMode: Bool { get }
     var threadsEnabled: Bool { get }
     var hideQuietNotificationAlerts: Bool { get }
+    
+    var voipPusherAppID: String { get }
+    var pushKitDeviceToken: String? { get }
+    var voipPushGatewayNotifyURL: String? { get }
 }
 
 nonisolated enum AppBuildType {
@@ -244,6 +248,28 @@ final nonisolated class AppSettings: @unchecked Sendable {
         pushGatewayBaseURL.appending(path: "_matrix/push/v1/notify")
     }
     
+    // HealthChat: the NSE lacks the notification filtering entitlement, so it cannot hand ringing
+    // calls to CallKit directly. Instead it asks the push gateway for a PushKit (VoIP) push, the
+    // way the legacy element-ios app did. The app persists what the NSE needs for that request
+    // here, because the NSE neither receives PushKit credentials nor runs the app settings hook.
+    
+    /// The push gateway app ID that delivers PushKit pushes (`push_type: voip` in Sygnal).
+    var voipPusherAppID: String {
+        #if DEBUG
+        InfoPlistReader.main.baseBundleIdentifier + ".ios.voip.dev"
+        #else
+        InfoPlistReader.main.baseBundleIdentifier + ".ios.voip.prod"
+        #endif
+    }
+    
+    /// The device's PushKit token, base64 encoded like the APNs pushkey.
+    @UserPreference
+    var pushKitDeviceToken: String?
+    
+    /// `pushGatewayNotifyEndpoint` as configured in the app, for the NSE.
+    @UserPreference
+    var voipPushGatewayNotifyURL: String?
+    
     @UserPreference(defaultValue: true)
     var enableNotifications: Bool