feat(auto): enable Android Auto messaging notifications

[riddlemd]

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Declare the app as a messaging app for Android Auto via the automotive app descriptor. This allows MessagingStyle notifications to surface on car head units. Users can now read and reply to mesh messages through Android Auto's native messaging
interface.

What changed

• Added app/src/main/res/xml/automotive_app_desc.xml declaring the notification category
• Added com.google.android.gms.car.application meta-data to AndroidManifest.xml pointing to the descriptor

How it works

The existing MeshServiceNotificationsImpl.createConversationNotification() already builds notifications with all the structure Android Auto requires — MessagingStyle, typed Person objects with unique keys, CATEGORY_MESSAGE, and wired ReplyReceiver / MarkAsReadReceiver actions. The only missing piece
was this manifest declaration telling the Android Auto host to look at the app's notifications at all.

With this change:

• Incoming mesh messages appear on the car's head unit
• The driver can reply by voice or quick text; replies are routed through the existing ReplyReceiver
• Messages are read aloud via TTS
• "Mark as read" dismisses from the car screen via the existing MarkAsReadReceiver

No new code paths, no new dependencies.

[jamesarich]

Hey - thanks, @riddlemd ! We've got a draft in progress with a bit richer eperience over on #5162 but this gets us the notifications until that lands.

[riddlemd]

Hey - thanks, @riddlemd ! We've got a draft in progress with a bit richer eperience over on #5162 but this gets us the notifications until that lands.

All good, someone on reddit noticed car play had support so I was looking into adding supported and realized how much of a lift it was gonna be so I figured I'd at least do the simple task of adding notifications.

[jamesarich]

car play had support

yep garth kicked off co-pilot to add auto support here too once he got it figured out on iOS 😂