Add iOS 27 remote media session and system player extension

RemoteShared/SystemPlayerCredentials.swift

@@ -0,0 +1,42 @@
+import Foundation
+import Security
+
+enum SystemPlayerCredentials {
+    private static func query(_ id: String) throws -> [String: Any] {
+        guard let group = Bundle.main.object(forInfoDictionaryKey: "MusicBridgeSharedKeychainGroup") as? String,
+              !group.isEmpty, !group.contains("$(") else {
+            throw BridgeError.message("Подпись приложения не настроила общий Keychain для системного пульта.")
+        }
+        return [kSecClass as String: kSecClassGenericPassword, kSecAttrService as String: "MusicBridge.system-player.v1",
+                kSecAttrAccount as String: id, kSecAttrAccessGroup as String: group]
+    }
+
+    static func save(_ connection: Connection, id: String) throws {
+        let query = try query(id)
+        let values: [String: Any] = [kSecValueData as String: try JSONEncoder().encode(connection),
+                                    kSecAttrAccessible as String: kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly]
+        var status = SecItemUpdate(query as CFDictionary, values as CFDictionary)
+        if status == errSecItemNotFound { status = SecItemAdd(query.merging(values) { _, v in v } as CFDictionary, nil) }
+        guard status == errSecSuccess else { throw failure(status) }
+    }
+
+    static func load(_ id: String) throws -> Connection {
+        var query = try query(id)
+        query[kSecReturnData as String] = true; query[kSecMatchLimit as String] = kSecMatchLimitOne
+        var item: CFTypeRef?
+        let status = SecItemCopyMatching(query as CFDictionary, &item)
+        guard status == errSecSuccess, let data = item as? Data else { throw failure(status) }
+        let saved = try JSONDecoder().decode(Connection.self, from: data)
+        guard let token = saved.token, Connection.isFingerprint(token) else { throw BridgeError.unauthorized }
+        return try Connection(endpoint: saved.endpoint.absoluteString, fingerprint: saved.fingerprint, token: token)
+    }
+
+    static func delete(_ id: String) throws {
+        let status = SecItemDelete(try query(id) as CFDictionary)
+        guard status == errSecSuccess || status == errSecItemNotFound else { throw failure(status) }
+    }
+
+    private static func failure(_ status: OSStatus) -> BridgeError {
+        .message("Системный пульт не получил доступ к Keychain (\(status)). Проверьте подпись приложения и расширения; обычный плеер остаётся доступен.")
+    }
+}