feature: localization (#32)

* build: add nlohmann/json library

* build(deps): add harfbuzz dependency

* feat(cmake): add guard to reject macOS builds

* feat(font): add HarfBuzz shaping and replace font with unifont

* feat(localization): add i18n support with en_US and zh_CN translations

Implement Localization class to load JSON translation files. Replace hardcoded strings in UI with translation keys and update sliders/combo buttons to use dynamic text.

* feat(localization): detect system locale for language default

* feat(settings): add language selection option with restart notification

* fix: use vckpg to add freetype on windows

assets/lang/zh_CN.json

@@ -0,0 +1,34 @@
+{
+    "menu.settings": "设置",
+    "menu.main.host_game": "创建游戏",
+    "menu.main.join_game": "加入游戏",
+    "menu.main.credits": "制作人员",
+    "menu.main.quit": "退出",
+    "menu.main.player_name": "玩家：{name}",
+    "menu.main.cubed_version": "Cubed：{version}",
+    "menu.pause.pause_menu": "暂停菜单",
+    "menu.pause.back_to_game": "返回游戏",
+    "menu.pause.return_to_main_menu": "返回主菜单",
+    "button.done": "完成",
+    "button.return": "返回",
+    "settings.title": "设置",
+    "settings.fov": "视野：{fov}",
+    "settings.mouse_sensitivity": "灵敏度：{sensitivity}",
+    "settings.distance": "距离：{distance}",
+    "settings.music_volume": "音乐：{music}",
+    "settings.sfx_volume": "音效：{sfx}",
+    "settings.fullscreen": "全屏：{state}",
+    "settings.aniso": "各向异性过滤：{aniso}",
+    "settings.vsync": "垂直同步: {state}",
+    "settings.language": "语言: {lang}",
+    "settings.restart_game_info": "您需要重启游戏以应用这些更改。",
+    "common.on": "开",
+    "common.off": "关",
+    "hostgame.create_a_new_world": "创建新世界",
+    "hostgame.world_seed": "世界种子",
+    "hostgame.port": "端口",
+    "hostgame.create_world": "创建世界",
+    "joingame.join_a_world": "加入世界",
+    "joingame.server_ip": "服务器IP",
+    "joingame.join_world": "加入世界"
+}