refactor: 重构 token 管理，新增 NATS adapter 和多示例

按照 TOKEN_REFACTOR.md / FIX_CONFIG.md 方案重构核心层：
- miot: Init() 优先读 storage token，新增 RefreshAuthInfo() 和刷新回调
- xiaomi: Config 改用 AuthInfo 结构体（含 UUID/UID/DataDir/OnTokenRefreshed）
- xiaomi: NewClient(ctx, Config) 新签名，新增 RefreshToken()，后台自动刷新
- xiaomi/devices: 设备控制接口重构
- 新增示例 12_ac_subscribe，其余示例适配新 Config

xiaomi/examples/12_ac_subscribe/data/cert/mihome_ca.cert

@@ -0,0 +1,21 @@
+-----BEGIN CERTIFICATE-----
+MIIBazCCAQ+gAwIBAgIEA/UKYDAMBggqhkjOPQQDAgUAMCIxEzARBgNVBAoTCk1p
+amlhIFJvb3QxCzAJBgNVBAYTAkNOMCAXDTE2MTEyMzAxMzk0NVoYDzIwNjYxMTEx
+MDEzOTQ1WjAiMRMwEQYDVQQKEwpNaWppYSBSb290MQswCQYDVQQGEwJDTjBZMBMG
+ByqGSM49AgEGCCqGSM49AwEHA0IABL71iwLa4//4VBqgRI+6xE23xpovqPCxtv96
+2VHbZij61/Ag6jmi7oZ/3Xg/3C+whglcwoUEE6KALGJ9vccV9PmjLzAtMAwGA1Ud
+EwQFMAMBAf8wHQYDVR0OBBYEFJa3onw5sblmM6n40QmyAGDI5sURMAwGCCqGSM49
+BAMCBQADSAAwRQIgchciK9h6tZmfrP8Ka6KziQ4Lv3hKfrHtAZXMHPda4IYCIQCG
+az93ggFcbrG9u2wixjx1HKW4DUA5NXZG0wWQTpJTbQ==
+-----END CERTIFICATE-----
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----

xiaomi/examples/12_ac_subscribe/main.go

@@ -0,0 +1,71 @@
+// Package main demonstrates AirConditioner.OnStateChanged subscription.
+// 运行后等待状态变化，Ctrl+C 退出。
+package main
+
+import (
+	"context"
+	"log"
+	"os"
+	"os/signal"
+
+	"xiaomihome/xiaomi"
+	"xiaomihome/xiaomi/devices"
+	miotconfig "xiaomihome/miot/examples/config"
+)
+
+func main() {
+	cfg, err := miotconfig.LoadConfig("../../../miot/examples/config.json")
+	if err != nil {
+		log.Fatal("请先运行 miot/examples/cloud_oauth 获取 token:", err)
+	}
+
+	client, err := xiaomi.NewClient(context.Background(), xiaomi.Config{
+		AuthInfo: xiaomi.AuthInfo{
+			AccessToken:  cfg.AuthInfo.AccessToken,
+			RefreshToken: cfg.AuthInfo.RefreshToken,
+			ExpiresIn:    cfg.AuthInfo.ExpiresIn,
+			ExpiresTS:    cfg.AuthInfo.ExpiresTS,
+		},
+		DataDir: "./data",
+		UUID:    cfg.UUID,
+		UID:     cfg.UID,
+	})
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer client.Close()
+
+	const targetDID = "2053225728"
+	info, err := client.GetDevice(context.Background(), targetDID)
+	if err != nil {
+		log.Fatalf("获取设备 %s 失败: %v", targetDID, err)
+	}
+	log.Printf("设备: %s (DID: %s, 型号: %s)", info.Name, info.DID, info.Model)
+
+	ac, err := devices.NewAirConditioner(client, info)
+	if err != nil {
+		log.Fatal("创建 AirConditioner 失败:", err)
+	}
+
+	// 先查一次当前状态
+	on, _ := ac.IsOn(context.Background())
+	log.Printf("初始状态: on=%v", on)
+
+	// 订阅状态变化
+	subID, err := ac.OnStateChanged(func(state devices.ACState, changed string) {
+		log.Printf("[%s] on=%v mode=%s target=%.1f current=%.1f fan=%s swing=%s",
+			changed, state.On, state.Mode, state.TargetTemperature, state.Temperature,
+			state.FanLevel, state.Swing)
+	})
+	if err != nil {
+		log.Printf("订阅失败: %v", err)
+	} else {
+		log.Printf("已订阅: subID=%s", subID)
+	}
+
+	log.Println("\n等待状态变化，Ctrl+C 退出...")
+	ch := make(chan os.Signal, 1)
+	signal.Notify(ch, os.Interrupt)
+	<-ch
+	log.Println("退出")
+}