Add achievement system with unlock and UI popup functionality (#8)

Autoloads/SteamManager.cs

@@ -0,0 +1,77 @@
+using System;
+using Godot;
+using Steamworks;
+using Steamworks.Data;
+
+namespace Mr.BrickAdventures.Autoloads;
+
+public partial class SteamManager : Node
+{
+    private const uint AppId = 3575090;
+    
+    public static string PlayerName { get; private set; } = "Player";
+    public static bool IsSteamInitialized { get; private set; } = false;
+
+    public override void _Ready()
+    {
+        try
+        {
+            SteamClient.Init(AppId);
+            IsSteamInitialized = true;
+
+            PlayerName = SteamClient.Name;
+
+            GD.Print($"Steam initialized successfully for user: {PlayerName}");
+        }
+        catch (Exception e)
+        {
+            GD.PushError("Failed to initialize Steamworks. Is Steam running?");
+            GD.PushError(e.Message);
+            IsSteamInitialized = false;
+        }
+    }
+
+    public override void _Process(double delta)
+    {
+        if (IsSteamInitialized) SteamClient.RunCallbacks();
+    }
+    
+    public override void _Notification(int what)
+    {
+        if (what == NotificationWMCloseRequest)
+        {
+            if (IsSteamInitialized)
+            {
+                SteamClient.Shutdown();
+            }
+            GetTree().Quit();
+        }
+    }
+
+    public static void UnlockAchievement(string achievementId)
+    {
+        if (!IsSteamInitialized)
+        {
+            GD.Print($"Steam not initialized. Cannot unlock achievement '{achievementId}'.");
+            return;
+        }
+
+        var ach = new Achievement(achievementId);
+
+        if (ach.State)
+        {
+            GD.Print($"Achievement '{achievementId}' is already unlocked.");
+            return;
+        }
+
+        if (ach.Trigger())
+        {
+            SteamUserStats.StoreStats();
+            GD.Print($"Successfully triggered achievement: {ach.Name} ({ach.Identifier})");
+        }
+        else
+        {
+            GD.PrintErr($"Failed to trigger achievement: {achievementId}");
+        }
+    }
+}