refactor: standardization round 2

- ConsoleManager: lazy GameManager/AchievementManager via Instance (fixes NullRef on console commands)
- AchievementManager, GhostManager: add static Instance property
- GhostEventHandler: use GhostManager.Instance, add _ExitTree unsubscription
- SpeedRunManager: remove unused IsVisible guard; TimeUpdated now emits when running
- SpeedRunHud: use SpeedRunManager.Instance, remove dead IsVisible binding
- SaveDataDto: moved to scripts/State/SaveDataDto.cs
- GameManager.AddCoins: XML doc clarifying permanent vs session coins

scripts/State/SaveDataDto.cs

@@ -0,0 +1,19 @@
+using System.Collections.Generic;
+
+namespace Mr.BrickAdventures.scripts.State;
+
+/// <summary>
+/// Serializable DTO for save data - no Godot types.
+/// </summary>
+public class SaveDataDto
+{
+    public int Version { get; set; }
+    public int Coins { get; set; }
+    public int Lives { get; set; }
+    public int CurrentLevel { get; set; }
+    public List<int> CompletedLevels { get; set; }
+    public List<int> UnlockedLevels { get; set; }
+    public List<string> UnlockedSkillNames { get; set; }
+    public List<string> UnlockedAchievements { get; set; }
+    public Dictionary<string, int> Statistics { get; set; }
+}