Add RollkofferSimulator iOS SpriteKit arcade game

Complete implementation of a 2D top-down arcade collector game where players
control a rolling suitcase through an airport, collecting good dogs and green
people while avoiding bad dogs and gray people.

Features:
- Touch & drag controls for suitcase movement
- Automatic scrolling airport floor with tile pattern
- 4 entity types: good dogs (small/big), bad dogs, green/gray humans
- Spawn system with configurable distribution rates
- Collision detection with visual feedback effects
- Score tracking with high score persistence
- 90-second time limit with 10 dogs + 5 humans goal
- 3 lives system with invincibility frames
- Menu, Game, GameOver, and Victory scenes
- German UI text (Created by Ingo K.)

Technical:
- iOS 15+ with SpriteKit framework
- Modular architecture with Nodes, Managers, Scenes
- Physics-based collision detection
- UserDefaults for score persistence

RollkofferSimulator/Models/GameState.swift

@@ -0,0 +1,103 @@
+//
+//  GameState.swift
+//  RollkofferSimulator
+//
+//  Created by Ingo K.
+//
+
+import Foundation
+
+/// Possible game states
+enum GameStateType {
+    case startScreen
+    case playing
+    case paused
+    case gameOver
+    case victory
+}
+
+/// Manages the current game state and statistics
+class GameState {
+
+    // MARK: - Properties
+    private(set) var currentState: GameStateType = .startScreen
+    private(set) var score: Int = 0
+    private(set) var lives: Int = Constants.startLives
+    private(set) var dogsCollected: Int = 0
+    private(set) var humansCollected: Int = 0
+    private(set) var timeRemaining: TimeInterval = Constants.gameTime
+
+    var isInvincible: Bool = false
+
+    // MARK: - Computed Properties
+    var hasWon: Bool {
+        return dogsCollected >= Constants.targetDogs &&
+               humansCollected >= Constants.targetHumans
+    }
+
+    var hasLost: Bool {
+        return lives <= 0 || (timeRemaining <= 0 && !hasWon)
+    }
+
+    // MARK: - State Management
+    func setState(_ state: GameStateType) {
+        currentState = state
+    }
+
+    func reset() {
+        score = 0
+        lives = Constants.startLives
+        dogsCollected = 0
+        humansCollected = 0
+        timeRemaining = Constants.gameTime
+        isInvincible = false
+        currentState = .playing
+    }
+
+    // MARK: - Score Management
+    func addPoints(_ points: Int) {
+        score += points
+    }
+
+    func collectDog() {
+        dogsCollected += 1
+    }
+
+    func collectHuman() {
+        humansCollected += 1
+    }
+
+    // MARK: - Lives Management
+    func loseLife() -> Bool {
+        guard !isInvincible else { return false }
+        lives -= 1
+        return true
+    }
+
+    // MARK: - Time Management
+    func updateTime(delta: TimeInterval) {
+        timeRemaining = max(0, timeRemaining - delta)
+    }
+
+    // MARK: - Formatted Strings
+    var formattedTime: String {
+        let seconds = Int(timeRemaining)
+        return "\(seconds)s"
+    }
+
+    var formattedScore: String {
+        return "SCORE: \(score)"
+    }
+
+    var formattedDogs: String {
+        return "🐕 \(dogsCollected)/\(Constants.targetDogs)"
+    }
+
+    var formattedHumans: String {
+        return "👤 \(humansCollected)/\(Constants.targetHumans)"
+    }
+
+    var formattedLives: String {
+        return String(repeating: "❤️", count: lives)
+    }
+}