feat(ruby-client): 新增 Ruby 客户端 SDK 及 demo，移除 C 语言支持

- 新增 kenaito-conf-ruby-client（Ruby 2.5+）及对应 demo
- 新增 Dockerfile.ruby
- README 技术栈移除 C，项目结构补充 Ruby 客户端
- README_EN.md 同步更新
- README_DOCKERFILE.md 补充 Ruby 构建命令

kenaito-conf-ruby-client/README_EN.md

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+# Kenaito Config Center Ruby Client
+
+[English](README_EN.md) | 中文
+
+Kenaito Config Center Ruby client SDK, compatible with Ruby 2.5+.
+
+## Installation
+
+### Option 1: Local Install
+
+```bash
+cd kenaito-conf-ruby-client
+gem build kenaito-conf.gemspec
+gem install kenaito-conf-1.0.3.gem
+```
+
+### Option 2: Bundler
+
+Add to your project `Gemfile`:
+
+```ruby
+gem 'kenaito-conf', path: '/path/to/kenaito-conf-ruby-client'
+```
+
+Then run:
+
+```bash
+bundle install
+```
+
+### Option 3: Direct Require
+
+```ruby
+require_relative '/path/to/kenaito-conf-ruby-client/lib/kenaito_conf'
+```
+
+## Usage Example
+
+```ruby
+require 'kenaito_conf'
+
+config = Kenaito::Conf::Config.new(
+  base_url: 'http://localhost:8080',
+  app_name: 'my-app',
+  env: 'daily',
+  sync_interval: 10
+)
+
+client = Kenaito::Conf::Client.new(config)
+
+# Listen for config changes
+client.on_change do |changed|
+  changed.each do |key, value|
+    puts "config changed: #{key} = #{value}"
+  end
+end
+
+# Start client (fetch configs)
+client.start
+
+# Get config
+value = client.get('database.host')
+all_configs = client.get_all
+
+# Manual sync once
+client.sync_once
+
+# Stop
+client.stop_client
+```
+
+## Configuration Options
+
+| Option | Description | Default |
+|--------|-------------|---------|
+| base_url | Config center backend URL | http://localhost:8080 |
+| app_name | Application name | empty |
+| env | Environment (dev/daily/prod) | dev |
+| version | Config version | latest |
+| token | Application token | empty |
+| sync_interval | Sync interval (seconds) | 10 |
+| ignore_global | Ignore global configs | false |
+| cache_dir | Cache directory | . |
+
+## Features
+
+- ✅ Full config fetch
+- ✅ Incremental sync
+- ✅ Local file cache for disaster recovery
+- ✅ Config change listener callback
+- ✅ Deleted config awareness (deletedKeys)