feat: 实现存档界面与场景切换，优化文字渲染

- 新增 SavePanel/SaveSlot 存档选择界面，支持已有存档与新建存档
- 新增 GameState 单例与 MainGame 入口，按参数区分新游戏/读档
- 主菜单接入中文字体，返回/进入存档面板流程打通
- 开启 2D/3D MSAA、TAA 与屏幕空间 AA，消除放大文字锯齿
- 设置 1920x1080 视口与中文本地化过滤

project.godot

@@ -17,13 +17,22 @@ config/icon="res://icon.svg"
 
 [display]
 
-window/size/window_mode=2
+window/size/viewport_width=1920
+window/size/viewport_height=1080
 window/stretch/mode="viewport"
+window/size/window_mode=2
 
 [dotnet]
 
 project/assembly_name="模拟宗门"
 
+[internationalization]
+
+locale/locale_filter_mode=1
+locale/script_filter=["Hans"]
+locale/country_filter=["CN"]
+locale/language_filter=[]
+
 [physics]
 
 3d/physics_engine="Jolt Physics"
@@ -31,3 +40,7 @@ project/assembly_name="模拟宗门"
 [rendering]
 
 rendering_device/driver.windows="d3d12"
+anti_aliasing/quality/msaa_2d=3
+anti_aliasing/quality/msaa_3d=3
+anti_aliasing/quality/screen_space_aa=2
+anti_aliasing/quality/use_taa=true