Add tier management system with JSON loading; refactor PopulationVisualizer for category handling

Scripts/Core/TierDto.cs

@@ -0,0 +1,15 @@
+using System.Collections.Generic;
+
+namespace ParasiticGod.Scripts.Core;
+
+public class TierDto
+{
+    public Follower.FollowerTier TierEnum { get; set; }
+    public long Threshold { get; set; }
+    public string ScenePath { get; set; }
+}
+
+public class TierListDto
+{
+    public List<TierDto> Tiers { get; set; }
+}