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-dotnet-client-demo/Program.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Collections.Generic;
+using KenaitoConf;
+
+var configValues = new Dictionary<string, string>
+{
+    { "database.host", Environment.GetEnvironmentVariable("DATABASE_HOST") ?? "192.168.1.1" },
+    { "database.port", Environment.GetEnvironmentVariable("DATABASE_PORT") ?? "8888" },
+    { "database.name", Environment.GetEnvironmentVariable("DATABASE_NAME") ?? "xxxx" },
+    { "database.user", Environment.GetEnvironmentVariable("DATABASE_USER") ?? "xxxx" },
+    { "database.password", Environment.GetEnvironmentVariable("DATABASE_PASSWORD") ?? "xxxxxxxx" },
+};
+
+var config = new Config
+{
+    BaseUrl = Environment.GetEnvironmentVariable("KENAITO_BASE_URL") ?? "http://localhost:8080",
+    AppName = Environment.GetEnvironmentVariable("KENAITO_APP_NAME") ?? "kenaito-springboot-demo",
+    Env = Environment.GetEnvironmentVariable("KENAITO_PROFILE") ?? "daily",
+    Version = Environment.GetEnvironmentVariable("KENAITO_VERSION") ?? "latest",
+    Token = Environment.GetEnvironmentVariable("KENAITO_TOKEN") ?? "",
+    SyncInterval = int.Parse(Environment.GetEnvironmentVariable("KENAITO_SYNC_INTERVAL") ?? "30"),
+    CacheDir = Environment.GetEnvironmentVariable("KENAITO_CACHE_DIR") ?? ".",
+};
+
+var client = new ConfigClient(config);
+
+client.OnChange(changed =>
+{
+    foreach (var kv in changed)
+    {
+        if (configValues.ContainsKey(kv.Key))
+        {
+            configValues[kv.Key] = kv.Value;
+            Console.Error.WriteLine($"config updated: {kv.Key} = {kv.Value}");
+        }
+    }
+});
+
+try
+{
+    await client.StartAsync();
+    var remote = client.GetAll();
+    foreach (var key in new List<string>(configValues.Keys))
+    {
+        if (remote.ContainsKey(key))
+            configValues[key] = remote[key];
+    }
+    Console.Error.WriteLine($"loaded {remote.Count} configs from remote");
+}
+catch (Exception e)
+{
+    Console.Error.WriteLine($"failed to init config client: {e.Message}");
+}
+
+Console.WriteLine("Current configs:");
+foreach (var kv in configValues)
+    Console.WriteLine($"  {kv.Key} = {kv.Value}");
+
+Console.WriteLine("\nListening for config changes... (press Ctrl+C to stop)");
+var cts = new System.Threading.CancellationTokenSource();
+Console.CancelKeyPress += (_, e) => { e.Cancel = true; cts.Cancel(); };
+try { await System.Threading.Tasks.Task.Delay(System.Threading.Timeout.Infinite, cts.Token); }
+catch (System.Threading.Tasks.TaskCanceledException) { }
+client.Stop();
+Console.WriteLine("Shutting down...");