Improve device picker cached refresh

[N0ahTM]

Summary

• Show cached device picker entries immediately before kicking off a fresh device enumeration.
• Add a small header refresh indicator for background refreshes while keeping the existing blocking spinner for first load.
• Cache plain device IDs/names in the picker view model instead of retaining DeviceInformation objects for later UI rebuilds.

Validation

• Rebased onto current origin/develop after command-line support landed.
• msbuild AudioPlaybackConnector2\\AudioPlaybackConnector2.vcxproj /p:Configuration=Debug /p:Platform=x64 /p:PreferredToolArchitecture=x64
• clang-format --dry-run --Werror AudioPlaybackConnector2/include/ui/DevicePickerViewModel.hpp AudioPlaybackConnector2/src/ui/DevicePickerViewModel.cpp AudioPlaybackConnector2/ui/DevicePickerView/DevicePickerView.xaml.cpp AudioPlaybackConnector2/ui/DevicePickerView/DevicePickerView.xaml.h
• cppcheck --enable=warning,performance,portability --std=c++20 --platform=win64 AudioPlaybackConnector2/src/
• Runtime smoke test from the packaged AppX debug output: app initialized, tray picker opened/closed, device selection triggered connect, and OpenAsync returned Success.

Notes

The GitHub build workflow currently runs only for PRs targeting main, so PRs targeting develop report no GitHub checks. Local build/static checks were run after rebasing onto develop.