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-demo/app.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+require_relative '../kenaito-conf-ruby-client/lib/kenaito_conf'
+
+config_values = {
+  'database.host' => ENV['DATABASE_HOST'] || '192.168.1.1',
+  'database.port' => ENV['DATABASE_PORT'] || '8888',
+  'database.name' => ENV['DATABASE_NAME'] || 'xxxx',
+  'database.user' => ENV['DATABASE_USER'] || 'xxxx',
+  'database.password' => ENV['DATABASE_PASSWORD'] || 'xxxxxxxx'
+}
+
+config = KenaitoConf::Config.new(
+  base_url: ENV['KENAITO_BASE_URL'] || 'http://localhost:8080',
+  app_name: ENV['KENAITO_APP_NAME'] || 'kenaito-springboot-demo',
+  env: ENV['KENAITO_PROFILE'] || 'daily',
+  version: ENV['KENAITO_VERSION'] || 'latest',
+  token: ENV['KENAITO_TOKEN'] || '',
+  sync_interval: (ENV['KENAITO_SYNC_INTERVAL'] || '30').to_i,
+  cache_dir: ENV['KENAITO_CACHE_DIR'] || '.'
+)
+
+client = KenaitoConf::ConfigClient.new(config)
+
+client.on_change do |changed|
+  changed.each do |k, v|
+    if config_values.key?(k)
+      config_values[k] = v
+      warn "config updated: #{k} = #{v}"
+    end
+  end
+end
+
+begin
+  client.start
+  remote = client.get_all
+  config_values.each_key do |k|
+    config_values[k] = remote[k] if remote[k]
+  end
+  warn "loaded #{remote.size} configs from remote"
+rescue StandardError => e
+  warn "failed to init config client: #{e.message}"
+end
+
+puts 'Current configs:'
+config_values.each do |k, v|
+  puts "  #{k} = #{v}"
+end
+
+puts "\nListening for config changes... (press Ctrl+C to stop)"
+sleep