docs: 记录遗嘱消息MAC解析方案

docs/superpowers/specs/2026-07-13-device-status-lwt-mac-design.md

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+# Device Status LWT MAC Resolution Design
+
+## Goal
+
+When a device publishes its MQTT last-will status on `/MAC/publish/status`, resolve the MAC address to the stored `deviceNo` before updating device status.
+
+## Design
+
+- Keep `DeviceStatusHandler` responsible for parsing status payloads and invoking status updates.
+- Reuse `DeviceIdentityResolver` to translate the Topic identity into an `AppDevice` and then its `deviceNo`.
+- The resolver first supports an existing `deviceNo` Topic and falls back to a case-insensitive `mac_address` lookup. This preserves compatibility while handling LWT Topics that contain a MAC address.
+- If no device matches the Topic identity, do not update any record; keep the existing warning log.
+- Update the handler documentation to state that the Topic identity may be either a device number or a MAC address.
+
+## Verification
+
+Add a focused unit test using the real `DeviceIdentityResolver` with a mocked `AppDeviceMapper`. The test publishes an offline status with a MAC identity and verifies that:
+
+1. The mapper looks up the MAC address.
+2. `MqttDeviceStatusService.markOffline` receives the resolved `deviceNo`.
+3. No status update uses the MAC address as a device number.
+
+## Scope
+
+This change only covers `/MAC/publish/status`. Other MQTT communication continues to use `deviceNo` according to the existing protocol.