Add nearby Find My tracker sound support

[Xare123]

Summary

• add a foreground-only Android scan for nearby Find My-compatible BLE accessories
• rank opaque candidates by signal strength and let the user select which nearby tracker to ring
• support DULT, Find My, and AirTag-compatible GATT sound command paths
• expose the action only for Android accessory rows in Find My

Privacy and safety

• no background scanning
• no Bluetooth addresses or advertisement payloads are returned to Dart
• candidates use opaque tokens that expire after 60 seconds
• the UI does not claim that a rotating BLE identifier maps to a particular iCloud Find My item

Validation

• focused Flutter tests pass (2/2)
• Android :app:compileAlphaDebugKotlin passes with Flutter 3.24.0 and Gradle 8.9
• analyzer reports only pre-existing warnings in findmy_page.dart

Remaining validation

This stays draft pending broader hardware-matrix testing across AirTag and compatible accessory firmware. Protocol compatibility was informed by the Apache-2.0 AirGuard implementation and is credited in the native handler.