feat: 新增 8 个语言客户端 SDK

- PHP 客户端 (kenaito-conf-php-client)
- .NET 客户端 (kenaito-conf-dotnet-client)
- C 客户端 (kenaito-conf-c-client)
- C++ 客户端 (kenaito-conf-cpp-client)
- Lua 客户端 (kenaito-conf-lua-client)
- Kotlin 客户端 (kenaito-conf-kotlin-client)
- Rust 客户端 (kenaito-conf-rust-client)
- Ruby 客户端 (kenaito-conf-ruby-client)

每个客户端包含完整的 SDK 实现和 demo 示例，支持：
- 配置拉取（全量/增量）
- AES-128-CBC 解密
- 本地缓存
- 变更回调
- Token 认证

更新根目录 README.md：
- 技术栈列表新增 8 种语言
- 项目结构新增 16 个目录
- 客户端接入章节新增 8 个使用示例

kenaito-conf-ruby-client/kenaito-conf.gemspec

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+Gem::Specification.new do |spec|
+  spec.name          = 'kenaito-conf'
+  spec.version       = '1.0.0'
+  spec.authors       = ['odboy']
+  spec.email         = ['tianjun@odboy.cn']
+
+  spec.summary       = 'Kenaito Config Center Ruby Client'
+  spec.description   = 'Ruby client for Kenaito Config Center'
+  spec.homepage      = 'https://gitea.odboy.cn/odboy/kenaito-conf'
+  spec.license       = 'MIT'
+
+  spec.required_ruby_version = '>= 2.7.0'
+
+  spec.files         = Dir['lib/**/*']
+  spec.require_paths = ['lib']
+end