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/fonts/OFL-1.1.txt

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+The SIL Open Font License version 1.1 is copied below, and is also
+available with a FAQ at http://scripts.sil.org/OFL.
+
+
+-----------------------------------------------------------
+SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
+-----------------------------------------------------------
+
+PREAMBLE
+The goals of the Open Font License (OFL) are to stimulate worldwide
+development of collaborative font projects, to support the font creation
+efforts of academic and linguistic communities, and to provide a free and
+open framework in which fonts may be shared and improved in partnership
+with others.
+
+The OFL allows the licensed fonts to be used, studied, modified and
+redistributed freely as long as they are not sold by themselves. The
+fonts, including any derivative works, can be bundled, embedded, 
+redistributed and/or sold with any software provided that any reserved
+names are not used by derivative works. The fonts and derivatives,
+however, cannot be released under any other type of license. The
+requirement for fonts to remain under this license does not apply
+to any document created using the fonts or their derivatives.
+
+DEFINITIONS
+"Font Software" refers to the set of files released by the Copyright
+Holder(s) under this license and clearly marked as such. This may
+include source files, build scripts and documentation.
+
+"Reserved Font Name" refers to any names specified as such after the
+copyright statement(s).
+
+"Original Version" refers to the collection of Font Software components as
+distributed by the Copyright Holder(s).
+
+"Modified Version" refers to any derivative made by adding to, deleting,
+or substituting -- in part or in whole -- any of the components of the
+Original Version, by changing formats or by porting the Font Software to a
+new environment.
+
+"Author" refers to any designer, engineer, programmer, technical
+writer or other person who contributed to the Font Software.
+
+PERMISSION & CONDITIONS
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the Font Software, to use, study, copy, merge, embed, modify,
+redistribute, and sell modified and unmodified copies of the Font
+Software, subject to the following conditions:
+
+1) Neither the Font Software nor any of its individual components,
+in Original or Modified Versions, may be sold by itself.
+
+2) Original or Modified Versions of the Font Software may be bundled,
+redistributed and/or sold with any software, provided that each copy
+contains the above copyright notice and this license. These can be
+included either as stand-alone text files, human-readable headers or
+in the appropriate machine-readable metadata fields within text or
+binary files as long as those fields can be easily viewed by the user.
+
+3) No Modified Version of the Font Software may use the Reserved Font
+Name(s) unless explicit written permission is granted by the corresponding
+Copyright Holder. This restriction only applies to the primary font name as
+presented to the users.
+
+4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
+Software shall not be used to promote, endorse or advertise any
+Modified Version, except to acknowledge the contribution(s) of the
+Copyright Holder(s) and the Author(s) or with their explicit written
+permission.
+
+5) The Font Software, modified or unmodified, in part or in whole,
+must be distributed entirely under this license, and must not be
+distributed under any other license. The requirement for fonts to
+remain under this license does not apply to any document created
+using the Font Software.
+
+TERMINATION
+This license becomes null and void if any of the above conditions are
+not met.
+
+DISCLAIMER
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
+OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
+COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
+DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
+OTHER DEALINGS IN THE FONT SOFTWARE.

assets/lang/en_US.json

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+{
+    "menu.settings": "Settings",
+    "menu.main.host_game": "Host Game",
+    "menu.main.join_game": "Join Game",
+    "menu.main.credits": "Credits",
+    "menu.main.quit": "Quit",
+    "menu.main.player_name": "Player: {name}",
+    "menu.main.cubed_version": "Cubed: {version}",
+    "menu.pause.pause_menu": "Pause Menu",
+    "menu.pause.back_to_game": "Back To Game",
+    "menu.pause.return_to_main_menu": "Return to Menu",
+    "button.done": "Done",
+    "button.return": "Return",
+    "settings.title": "Settings",
+    "settings.fov": "Fov: {fov}",
+    "settings.mouse_sensitivity": "Sensitivity: {sensitivity}",
+    "settings.distance": "Distance: {distance}",
+    "settings.music_volume": "Music: {music}",
+    "settings.sfx_volume": "SFX: {sfx}",
+    "settings.fullscreen": "fullscreen: {state}",
+    "settings.aniso": "Aniso: {aniso}",
+    "settings.vsync": "V-Sync: {state}",
+    "settings.language": "Language: {lang}",
+    "settings.restart_game_info": "You need to restart the game to apply this changes.",
+    "common.on": "on",
+    "common.off": "off",
+    "hostgame.create_a_new_world": "Create A New World",
+    "hostgame.world_seed": "World Seed",
+    "hostgame.port": "Port",
+    "hostgame.create_world": "Create World",
+    "joingame.join_a_world": "Join A World",
+    "joingame.server_ip": "Server Ip",
+    "joingame.join_world": "Join World"
+}

assets/lang/zh_CN.json

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+{
+    "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"
+}