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/04_light_control/main.go

@@ -22,10 +22,15 @@ func main() {
 	}
 
 	client, err := xiaomi.NewClient(ctx, xiaomi.Config{
-		ClientSecret: "",
-		AccessToken:  cfg.AuthInfo.AccessToken,
-		UID:          cfg.UID,
-		UUID:         cfg.UUID,
+		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)
@@ -88,9 +93,10 @@ func main() {
 		log.Printf("当前颜色: R=%d G=%d B=%d", r, g, b)
 	}
 
-	subID, err := lt.OnStateChanged(func(state devices.LightState) {
-		log.Printf("灯光状态变化: power=%v brightness=%d colorTemp=%dK rgb=[%d,%d,%d]",
-			state.Power, state.Brightness, state.ColorTemp,
+	subID, err := lt.OnStateChanged(func(state devices.LightState, changed string) {
+		log.Printf("灯光状态变化: %s → on=%v brightness=%d colorTemp=%dK rgb=[%d,%d,%d]",
+			changed,
+			state.On, state.Brightness, state.ColorTemperature,
 			state.ColorRGB[0], state.ColorRGB[1], state.ColorRGB[2])
 	})
 	if err != nil {