Send media audio to the car without a per-drive prompt

The head unit offers a media sink, but Android answers Setup with an
empty reply instead of a Config message. AudioLink now falls back to
the advertised sink after 2.5s. AudioCaptureService captures by audio
usage, not by app, so switching media apps costs nothing further and
one grant covers a whole drive.

A one-time adb command (PROJECT_MEDIA) removes the consent dialog
itself; the setup screen now includes it as a copyable step, next to
the existing mic-permission step.

Capture counts as a screen share, so Android 15 hides notification
contents while it runs. ScreenShareGuard lifts that protection for
the length of the capture, with a second adb grant
(WRITE_SECURE_SETTINGS), and restores it afterward, including after a
crash.

The phone keeps playing what it captures, so AudioCaptureService also
mutes STREAM_MUSIC for the drive and restores it on every exit path.

Adds a debug bench (BenchAudioSink, CarPreviewActivity --ez audio
true) for testing the audio path without a car, and a unit test that
rebuilds the real head unit's ServiceDiscoveryResponse from a logged
session to confirm the media and guidance sinks are found correctly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarSettingsScreen.kt

@@ -98,9 +98,10 @@ fun CarSettingsScreen() {
             pipeAudio,
         ) { CarSettings.setPipeAudio(it) }
         Text(
-            "Phone output needs no permission: the app plays as it normally would, e.g. over " +
-                "Bluetooth to the car. Through Gearslip sends the sound over the car link, and " +
-                "Android asks for screen-capture consent each time.",
+            "Through Gearslip sends the sound over the USB link. Android asks for consent the " +
+                "first time a media app plays in the car, and some apps refuse to be captured at " +
+                "all. Phone output needs no permission: the app plays as it normally would, for " +
+                "example over Bluetooth to the car.",
             style = MaterialTheme.typography.bodySmall,
             color = MaterialTheme.colorScheme.onSurfaceVariant,
         )