feat: Add variable system, scene transition, and improve character layout

- **Introduce Variable System**
  - Added singleton class for variable management
  - Implemented script commands `[var]` and `[add]` for variable control
  - Supported variable substitution (`{variable}`) in dialogue and choices

- **Expand Script Features**
  - Added `[scene]` command for scene transition (load scene and link next script)

- **Improve Character Presentation**
  - Refactored character object hierarchy for better animation control
  - Applied mask-based soft transition effect (Soft Wipe) for expression changes

Assets/_MAIN/Scripts/Core/ScriptParser.cs

@@ -1,6 +1,5 @@
 using System.Collections.Generic;
 using System.Text.RegularExpressions;
-using UnityEngine;
 
 public class ScriptParser
 {
@@ -32,7 +31,6 @@ public class ScriptParser
             {
                 string tagName = tagMatch.Groups[1].Value;
                 string attrString = tagMatch.Groups[2].Value;
-                Debug.Log($"ScriptParser :: Tag: {tagName} {attrString}");
 
                 var scriptAction = new ScriptAction { Type = tagName };