Add PICK intent for launching with exolist.json

This works around the issue described in #438

demos/main/src/main/AndroidManifest.xml

@@ -52,6 +52,7 @@
       </intent-filter>
       <intent-filter>
         <action android:name="android.intent.action.VIEW"/>
+        <action android:name="androidx.media3.demo.main.action.BROWSE"/>
         <category android:name="android.intent.category.DEFAULT"/>
         <category android:name="android.intent.category.BROWSABLE"/>
         <data android:scheme="http"/>