Add Sonos speaker control: location-aware playback and speaker selection

SonosManager talks to Sonos speakers on the LAN; PlayMusicOnSonos and
SpeakerLocation add location-aware "play on the nearest speaker" logic.
ContentView and Speaker_ListensApp wire it into the app shell; the
default SwiftData Item.swift scaffold is removed since this isn't a
data-list app. Adds AppShortcuts/Localizable string catalogs and a
custom app icon.