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/AndroidManifest.xml

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools">
 
     <!-- The projected WebView loads real pages; without this every load fails silently. -->
     <uses-permission android:name="android.permission.INTERNET" />
@@ -23,6 +24,21 @@
     <!-- Capturing a media app's playback (to send to the car) is gated on this by the platform. -->
     <uses-permission android:name="android.permission.RECORD_AUDIO" />
 
+    <!--
+        Playback capture copies a stream rather than moving it, so the phone keeps playing the
+        music it is sending to the car. Silencing the phone's own speaker for the drive needs this.
+    -->
+    <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />
+
+    <!--
+        Audio capture counts as a screen share, and Android hides notifications during one. The
+        protection can be switched off for the drive, but only with this, granted once over adb
+        (pm grant). Without it Gearslip works the same and notifications stay hidden.
+    -->
+    <uses-permission
+        android:name="android.permission.WRITE_SECURE_SETTINGS"
+        tools:ignore="ProtectedPermissions" />
+
     <!--
       Declared, not just requested. Templated apps decide whether to talk to a host by asking
       whether it holds this permission (HostValidator.isValidHost checks it before falling back