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/VariableManager.cs

@@ -0,0 +1,73 @@
+using System.Collections.Generic;
+using UnityEngine;
+
+public class VariableManager
+{
+    private static VariableManager _instance;
+    public static VariableManager Instance => _instance ??= new VariableManager();
+
+    private Dictionary<string, object> _variables = new();
+
+    public void SetVariable(string name, string value)
+    {
+        // Try to parse as int or float, otherwise string
+        if (int.TryParse(value, out int intVal))
+            _variables[name] = intVal;
+        else if (float.TryParse(value, out float floatVal))
+            _variables[name] = floatVal;
+        else
+            _variables[name] = value;
+
+
+        Debug.Log($"VariableManager :: Set {name} = {_variables[name]} ({_variables[name].GetType()})");
+    }
+
+    public object GetVariable(string name)
+    {
+        return _variables.ContainsKey(name) ? _variables[name] : null;
+    }
+
+    public void AddVariable(string name, string valueStr)
+    {
+        if (!_variables.ContainsKey(name))
+        {
+            SetVariable(name, valueStr);
+            return;
+        }
+
+        object current = _variables[name];
+
+
+        if (current is int currentInt && int.TryParse(valueStr, out int addInt))
+        {
+            _variables[name] = currentInt + addInt;
+        }
+        else if (current is float currentFloat && float.TryParse(valueStr, out float addFloat))
+        {
+            _variables[name] = currentFloat + addFloat;
+        }
+        else if (current is string currentStr)
+        {
+            _variables[name] = currentStr + valueStr;
+        }
+        else
+        {
+            Debug.LogWarning($"VariableManager :: Cannot add {valueStr} to {name} (Type: {current.GetType()})");
+        }
+
+
+        Debug.Log($"VariableManager :: Add {name} += {valueStr} -> {_variables[name]}");
+    }
+
+
+    public string ReplaceVariables(string text)
+    {
+        if (string.IsNullOrEmpty(text)) return text;
+
+        foreach (var kvp in _variables)
+        {
+            text = text.Replace($"{{{kvp.Key}}}", kvp.Value.ToString());
+        }
+        return text;
+    }
+}