feat: implement Live Activity registration service and enhance notifications handling

Mayday/Services/DevicePlatform.swift

@@ -0,0 +1,25 @@
+import Foundation
+
+/// Wire-format identifiers for the `platform` field on the notification
+/// service's `/devices` endpoint. Kept in sync with the backend's
+/// `model.DevicePlatform` constants.
+enum DevicePlatform {
+    static let ios = "ios"
+    static let iosLiveActivityStart = "ios-liveactivity"
+
+    /// Builds a per-activity update token platform tag. The suffix is the
+    /// `alertId` the Activity was started for, used by the backend to target
+    /// update/end pushes at a specific running Live Activity.
+    static func iosLiveActivityUpdate(alertId: String) -> String {
+        "ios-liveactivity-\(alertId)"
+    }
+}
+
+enum DeviceTokenFormatter {
+    /// APNs returns the device token as raw bytes; the HTTP/2 endpoint expects
+    /// a lowercase hex string. Used uniformly for APNs, Push-to-Start and
+    /// per-activity update tokens.
+    static func hex(_ data: Data) -> String {
+        data.map { String(format: "%02.2hhx", $0) }.joined()
+    }
+}