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

ProjectSettings/EditorBuildSettings.asset

@@ -8,6 +8,9 @@ EditorBuildSettings:
   - enabled: 1
     path: Assets/_MAIN/Scenes/VisualNovel.unity
     guid: 199e3baed267a4c4fb4665bdaf82e49c
+  - enabled: 1
+    path: Assets/_MAIN/Scenes/Scene01.unity
+    guid: ab7661506d731e6428485450843b0c2c
   m_configObjects:
     com.unity.input.settings.actions: {fileID: -944628639613478452, guid: 052faaac586de48259a63d0c4782560b, type: 3}
   m_UseUCBPForAssetBundles: 0