DND silences the media stream by default, so playback on STREAM_MUSIC was
invisible during DND even though the notification showed. Switch to
STREAM_ALARM + USAGE_ALARM, which DND exempts by default, and restore/force
the alarm stream volume instead of media.
Adds a Settings screen (SettingsActivity) where the user configures:
- the SMS trigger phrase (replaces hardcoded RING_NOW/PLAY_SONG)
- the sound: system ringtone (with picker) or a picked audio file
- the play duration (5-300s, replaces the fixed 30s)
Values persist via RingConfig (SharedPreferences). SmsReceiver matches the
configured phrase; RingService plays the stored Uri for the configured length.
Removes the old MediaStore by-name song search and its hardcoded duration.
