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-php-client-demo/app.php

@@ -0,0 +1,61 @@
+<?php
+
+require_once __DIR__ . '/../kenaito-conf-php-client/autoload.php';
+
+use KenaitoConf\Config;
+use KenaitoConf\ConfigClient;
+
+$configValues = [
+    'database.host' => getenv('DATABASE_HOST') ?: '192.168.1.1',
+    'database.port' => getenv('DATABASE_PORT') ?: '8888',
+    'database.name' => getenv('DATABASE_NAME') ?: 'xxxx',
+    'database.user' => getenv('DATABASE_USER') ?: 'xxxx',
+    'database.password' => getenv('DATABASE_PASSWORD') ?: 'xxxxxxxx',
+];
+
+$config = new Config([
+    'baseUrl' => getenv('KENAITO_BASE_URL') ?: 'http://localhost:8080',
+    'appName' => getenv('KENAITO_APP_NAME') ?: 'kenaito-springboot-demo',
+    'env' => getenv('KENAITO_PROFILE') ?: 'daily',
+    'version' => getenv('KENAITO_VERSION') ?: 'latest',
+    'token' => getenv('KENAITO_TOKEN') ?: '',
+    'syncInterval' => (int)(getenv('KENAITO_SYNC_INTERVAL') ?: 30),
+    'cacheDir' => getenv('KENAITO_CACHE_DIR') ?: '.',
+]);
+
+$client = new ConfigClient($config);
+
+$client->onChange(function ($changed) use (&$configValues) {
+    foreach ($changed as $k => $v) {
+        if (isset($configValues[$k])) {
+            $configValues[$k] = $v;
+            error_log("config updated: {$k} = {$v}");
+        }
+    }
+});
+
+try {
+    $client->start();
+    $remote = $client->getAll();
+    foreach ($configValues as $k => &$v) {
+        if (isset($remote[$k])) {
+            $v = $remote[$k];
+        }
+    }
+    error_log("loaded " . count($remote) . " configs from remote");
+} catch (Exception $e) {
+    error_log("failed to init config client: " . $e->getMessage());
+}
+
+$port = (int)(getenv('SERVER_PORT') ?: 8084);
+
+echo "Server started on port {$port}\n";
+echo "Current configs:\n";
+foreach ($configValues as $k => $v) {
+    echo "  {$k} = {$v}\n";
+}
+
+while (true) {
+    pcntl_signal_dispatch();
+    usleep(100000);
+}