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/devices/fan.go

@@ -20,6 +20,16 @@ type Fan interface {
 
 	SetNaturalWind(ctx context.Context, on bool) error
 	IsNaturalWind(ctx context.Context) (bool, error)
+
+	OnStateChanged(handler func(state FanState, changed string)) (string, error)
+}
+
+// FanState 风扇完整状态（MQTT 缓存）
+type FanState struct {
+	On          bool `json:"on"`
+	FanLevel    int  `json:"fanLevel"`
+	Oscillation bool `json:"oscillation"`
+	NaturalWind bool `json:"naturalWind"`
 }
 
 type fanDevice struct {
@@ -28,6 +38,8 @@ type fanDevice struct {
 	propFanLevel    siidPiid // "fan-level"
 	propOscillation siidPiid // "horizontal-swing" or "oscillation"
 	propNaturalWind siidPiid // "mode" (natural wind mode)
+
+	stateCache FanState
 }
 
 // NewFan creates a Fan control for the given device.
@@ -148,3 +160,36 @@ func (d *fanDevice) IsNaturalWind(ctx context.Context) (bool, error) {
 	}
 	return toInt(prop.Value) == 1, nil
 }
+
+func (d *fanDevice) OnStateChanged(handler func(state FanState, changed string)) (string, error) {
+	type field struct{ siid, piid int; name string; fill func(*FanState, interface{}) }
+	var fields []field
+	if d.propOn.valid {
+		fields = append(fields, field{d.propOn.siid, d.propOn.piid, "on",
+			func(s *FanState, v interface{}) { s.On, _ = v.(bool) }})
+	}
+	if d.propFanLevel.valid {
+		fields = append(fields, field{d.propFanLevel.siid, d.propFanLevel.piid, "fan-level",
+			func(s *FanState, v interface{}) { s.FanLevel = toInt(v) }})
+	}
+	if d.propOscillation.valid {
+		fields = append(fields, field{d.propOscillation.siid, d.propOscillation.piid, "swing",
+			func(s *FanState, v interface{}) { s.Oscillation, _ = v.(bool) }})
+	}
+	if d.propNaturalWind.valid {
+		fields = append(fields, field{d.propNaturalWind.siid, d.propNaturalWind.piid, "mode",
+			func(s *FanState, v interface{}) { s.NaturalWind = toInt(v) == 1 }})
+	}
+	if len(fields) == 0 {
+		return "", xiaomi.ErrNotSupported
+	}
+	return d.SubProp(0, 0, func(did string, prop *xiaomi.PropertyValue) {
+		for _, f := range fields {
+			if f.siid == prop.SIID && f.piid == prop.PIID {
+				f.fill(&d.stateCache, prop.Value)
+				handler(d.stateCache, f.name)
+				return
+			}
+		}
+	})
+}