feat: implement Live Activity registration service and enhance notifications handling

Mayday/Models/AlertAttributes.swift

@@ -14,9 +14,61 @@ struct AlertAttributes: ActivityAttributes {
         let updatedAt: Date
 
         enum CodingKeys: String, CodingKey {
-            case title, value, status
-            case startedAt = "startedAt"
-            case updatedAt = "updatedAt"
+            case title, value, status, startedAt, updatedAt
+        }
+
+        init(title: String, value: String?, status: AlertStatus, startedAt: Date, updatedAt: Date) {
+            self.title = title
+            self.value = value
+            self.status = status
+            self.startedAt = startedAt
+            self.updatedAt = updatedAt
+        }
+
+        init(from decoder: Decoder) throws {
+            let c = try decoder.container(keyedBy: CodingKeys.self)
+            title = try c.decode(String.self, forKey: .title)
+            value = try c.decodeIfPresent(String.self, forKey: .value)
+            status = try c.decode(AlertStatus.self, forKey: .status)
+            startedAt = try Self.decodeDate(from: c, forKey: .startedAt)
+            updatedAt = try Self.decodeDate(from: c, forKey: .updatedAt)
+        }
+
+        func encode(to encoder: Encoder) throws {
+            var c = encoder.container(keyedBy: CodingKeys.self)
+            try c.encode(title, forKey: .title)
+            try c.encodeIfPresent(value, forKey: .value)
+            try c.encode(status, forKey: .status)
+            try c.encode(Self.isoFormatter.string(from: startedAt), forKey: .startedAt)
+            try c.encode(Self.isoFormatter.string(from: updatedAt), forKey: .updatedAt)
+        }
+
+        // ActivityKit uses the default JSONDecoder when materialising ContentState
+        // from a remote push payload, so dates round-trip as ISO8601 strings
+        // matching the backend's time.RFC3339[Nano] output. Both formatters are
+        // pre-built and treated as immutable; ISO8601DateFormatter is documented
+        // thread-safe for read use.
+        nonisolated(unsafe) private static let isoWithFractional: ISO8601DateFormatter = {
+            let f = ISO8601DateFormatter()
+            f.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
+            return f
+        }()
+        nonisolated(unsafe) private static let isoWithoutFractional: ISO8601DateFormatter = {
+            let f = ISO8601DateFormatter()
+            f.formatOptions = [.withInternetDateTime]
+            return f
+        }()
+        // Single shared encoder format: ISO8601 without fractional seconds,
+        // since iOS reconstructs Date from string and sub-second precision is
+        // irrelevant for the alert timestamps we surface.
+        private static var isoFormatter: ISO8601DateFormatter { isoWithoutFractional }
+
+        private static func decodeDate(from c: KeyedDecodingContainer<CodingKeys>, forKey key: CodingKeys) throws -> Date {
+            let s = try c.decode(String.self, forKey: key)
+            if let d = isoWithFractional.date(from: s) ?? isoWithoutFractional.date(from: s) {
+                return d
+            }
+            throw DecodingError.dataCorruptedError(forKey: key, in: c, debugDescription: "Invalid ISO8601 date: \(s)")
         }
     }
 }