fix(xiaomi): 空调风速按数字档位映射并增加 MQTT 反向语义解析

klwdz1.airc.001 等设备 fan-level 枚举为 Auto + Level1~Level5，SDK 侧
low/medium/high 在枚举里查不到，导致只有 Auto 能设置成功。

- valMapper 增加 levelFallback 开关（仅 fan-level 启用）：精确匹配失败时
  low/medium/high 按数字档位相对位置映射（排除 Auto=0）
- name() 增加对称的反向映射：设备上报 1/3/5 → low/medium/high，
  控制与 MQTT 通知使用同一套语义枚举
- newValMapper 默认关闭 fallback，mode/swing 行为不变
- 新增 TestValMapperLevelFallback 覆盖正反向映射与 mode 无副作用

xiaomi/devices/devices_test.go

@@ -3,6 +3,7 @@ package devices
 import (
 	"testing"
 
+	"xiaomihome/miot"
 	"xiaomihome/xiaomi"
 )
 
@@ -200,3 +201,43 @@ func TestServiceShortName(t *testing.T) {
 		}
 	}
 }
+
+func TestValMapperLevelFallback(t *testing.T) {
+	// klwdz1.airc.001 场景：Auto + Level1~Level5
+	vl := miot.MIoTSpecValueList{
+		{Value: 0, Desc: "Auto"}, {Value: 1, Desc: "Level1"}, {Value: 2, Desc: "Level2"},
+		{Value: 3, Desc: "Level3"}, {Value: 4, Desc: "Level4"}, {Value: 5, Desc: "Level5"},
+	}
+	vm := newValMapperLevel(vl)
+	cases := []struct{ name string; want int; ok bool }{
+		{"auto", 0, true}, {"Auto", 0, true},
+		{"low", 1, true}, {"medium", 3, true}, {"high", 5, true},
+		{"level3", 3, true},
+	}
+	for _, c := range cases {
+		got, ok := vm.val(c.name)
+		if ok != c.ok || (ok && got != c.want) {
+			t.Errorf("val(%q) = (%d,%v), want (%d,%v)", c.name, got, ok, c.want, c.ok)
+		}
+	}
+	// 反向解析（MQTT 上报值 → 语义枚举），与 val() 正向对称
+	rname := []struct{ v int; want string }{
+		{0, "auto"}, {1, "low"}, {3, "medium"}, {5, "high"}, {2, "Level2"},
+	}
+	for _, c := range rname {
+		if got := vm.name(c.v); got != c.want {
+			t.Errorf("name(%d) = %q, want %q", c.v, got, c.want)
+		}
+	}
+	// mode 枚举不受影响（无 low/medium/high fallback 副作用）
+	mvl := miot.MIoTSpecValueList{
+		{Value: 0, Desc: "Auto"}, {Value: 1, Desc: "Cool"}, {Value: 2, Desc: "Heat"},
+	}
+	mvm := newValMapper(mvl)
+	if _, ok := mvm.val("low"); ok {
+		t.Error("mode mapper should not resolve 'low'")
+	}
+	if v, ok := mvm.val("cool"); !ok || v != 1 {
+		t.Errorf("mode val(cool) = (%d,%v), want (1,true)", v, ok)
+	}
+}