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-kotlin-client-demo/build.gradle.kts

@@ -0,0 +1,14 @@
+plugins {
+    kotlin("jvm") version "1.9.0"
+    application
+}
+
+repositories { mavenCentral() }
+
+dependencies {
+    implementation(files("../kenaito-conf-kotlin-client/build/libs/kenaito-conf-kotlin-client-1.0.0.jar"))
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.7.3")
+    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.6.0")
+}
+
+application { mainClass.set("demo.AppKt") }

kenaito-conf-kotlin-client-demo/settings.gradle.kts

@@ -0,0 +1 @@
+rootProject.name = "kenaito-conf-kotlin-client-demo"

kenaito-conf-kotlin-client-demo/src/main/kotlin/demo/App.kt

@@ -0,0 +1,49 @@
+import kenait.conf.Config
+import kenait.conf.ConfigClient
+
+fun main() {
+    val configValues = mutableMapOf(
+        "database.host" to (System.getenv("DATABASE_HOST") ?: "192.168.1.1"),
+        "database.port" to (System.getenv("DATABASE_PORT") ?: "8888"),
+        "database.name" to (System.getenv("DATABASE_NAME") ?: "xxxx"),
+        "database.user" to (System.getenv("DATABASE_USER") ?: "xxxx"),
+        "database.password" to (System.getenv("DATABASE_PASSWORD") ?: "xxxxxxxx"),
+    )
+
+    val config = Config(
+        baseUrl = System.getenv("KENAITO_BASE_URL") ?: "http://localhost:8080",
+        appName = System.getenv("KENAITO_APP_NAME") ?: "kenaito-springboot-demo",
+        env = System.getenv("KENAITO_PROFILE") ?: "daily",
+        version = System.getenv("KENAITO_VERSION") ?: "latest",
+        token = System.getenv("KENAITO_TOKEN") ?: "",
+        syncInterval = (System.getenv("KENAITO_SYNC_INTERVAL") ?: "30").toInt(),
+        cacheDir = System.getenv("KENAITO_CACHE_DIR") ?: ".",
+    )
+
+    val client = ConfigClient(config)
+
+    client.onChange { changed ->
+        changed.forEach { (k, v) ->
+            if (configValues.containsKey(k)) {
+                configValues[k] = v
+                System.err.println("config updated: $k = $v")
+            }
+        }
+    }
+
+    try {
+        client.start()
+        val remote = client.getAll()
+        configValues.keys.forEach { k ->
+            remote[k]?.let { configValues[k] = it }
+        }
+        System.err.println("loaded ${remote.size} configs from remote")
+    } catch (e: Exception) {
+        System.err.println("failed to init config client: ${e.message}")
+    }
+
+    println("Current configs:")
+    configValues.forEach { (k, v) -> println("  $k = $v") }
+    println("\nListening for config changes... (press Ctrl+C to stop)")
+    Thread.currentThread().join()
+}