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-lua-client/client.lua

@@ -0,0 +1,120 @@
+local http = require("socket.http")
+local ltn12 = require("ltn12")
+local cjson = require("cjson")
+local openssl = require("openssl")
+
+local ConfigClient = {}
+ConfigClient.__index = ConfigClient
+
+function ConfigClient.new(config)
+    local self = setmetatable({}, ConfigClient)
+    self.config = config or {}
+    self.config.baseUrl = self.config.baseUrl or ""
+    self.config.appName = self.config.appName or ""
+    self.config.env = self.config.env or "dev"
+    self.config.version = self.config.version or "latest"
+    self.config.token = self.config.token or ""
+    self.config.syncInterval = self.config.syncInterval or 60
+    self.config.ignoreGlobal = self.config.ignoreGlobal or false
+    self.config.cacheDir = self.config.cacheDir or "."
+    
+    self.configs = {}
+    self.secret = ""
+    self.globalSecret = ""
+    self.lastTime = 0
+    self.handlers = {}
+    return self
+end
+
+function ConfigClient:on_change(handler)
+    table.insert(self.handlers, handler)
+end
+
+function ConfigClient:get(key)
+    return self.configs[key]
+end
+
+function ConfigClient:get_all()
+    return self.configs
+end
+
+local function decrypt_config(secret, data)
+    local prefix = "{Cipher}"
+    if string.sub(data, 1, #prefix) ~= prefix then
+        return data
+    end
+    local encrypted = string.sub(data, #prefix + 1)
+    
+    -- MD5 hash
+    local md5_hash = openssl.digest("md5", secret)
+    local aes_key = string.sub(md5_hash, 17)
+    
+    -- Base64 decode
+    local cipher_text = openssl.base64(encrypted, false)
+    
+    -- AES-128-CBC decrypt
+    local iv = string.rep("\0", 16)
+    local cipher = openssl.cipher.new("aes-128-cbc")
+    local plain_text = cipher:decrypt(cipher_text, aes_key, iv)
+    
+    -- Remove PKCS7 padding
+    local padding = string.byte(plain_text, -1)
+    return string.sub(plain_text, 1, -padding - 1)
+end
+
+function ConfigClient:start()
+    -- Fetch all configs
+    local url = self.config.baseUrl .. "/api/fetchAllConfigs"
+    local payload = cjson.encode({
+        appName = self.config.appName,
+        env = self.config.env,
+        version = self.config.version,
+        ignoreGlobal = self.config.ignoreGlobal,
+        token = self.config.token
+    })
+    
+    local response_body = {}
+    local res, code, response_headers = http.request{
+        url = url,
+        method = "POST",
+        headers = {
+            ["Content-Type"] = "application/json",
+            ["Content-Length"] = #payload
+        },
+        source = ltn12.source.string(payload),
+        sink = ltn12.sink.table(response_body)
+    }
+    
+    if code == 200 then
+        local data = cjson.decode(table.concat(response_body))
+        
+        if data["kenaito.config.encrypt-secret"] then
+            self.secret = data["kenaito.config.encrypt-secret"]
+        end
+        if data["kenaito.config.global-encrypt-secret"] then
+            self.globalSecret = data["kenaito.config.global-encrypt-secret"]
+        end
+        if data["latest.fetch.timestamp"] then
+            self.lastTime = tonumber(data["latest.fetch.timestamp"])
+        end
+        
+        for k, v in pairs(data) do
+            if not string.match(k, "^kenaito%.") and k ~= "latest.fetch.timestamp" then
+                if type(v) == "string" then
+                    self.configs[k] = decrypt_config(self.secret, v)
+                    if self.configs[k] == v and self.globalSecret ~= "" then
+                        self.configs[k] = decrypt_config(self.globalSecret, v)
+                    end
+                end
+            end
+        end
+        
+        print("[ConfigClient] fetched " .. #self.configs .. " configs")
+    end
+end
+
+function ConfigClient:stop()
+    -- Cleanup
+end
+
+return ConfigClient