…car-app to stable

The car feature shipped against androidx.car.app 1.9.0-alpha01 with several
surfaces built but never wired, plus a latent crash once pinned to stable.

🐛 Fixes
- HomeScreen built TabTemplate without setActiveTabContentId(), which throws on
  stable 1.7.0 — the tabbed car UI would crash on launch for every connected user.
- Messaging notifications never reached Android Auto: the manifest was missing the
  com.google.android.gms.car.application meta-data pointing at automotive_app_desc.
- meshName showed the firmware version string instead of the owner long name.

🌟 Wiring
- Emergency flow: ALERT_APP packets now drive EmergencyHandler (was emptyFlow()).
- Reply / mark-read notification actions now carry the Android Auto semantic actions
  (SEMANTIC_ACTION_REPLY / _MARK_AS_READ + setShowsUserInterface(false)) at the source
  in core MeshNotificationManagerImpl, so the app's existing MessagingStyle
  notifications work hands-free in-car.

🧹 Cleanup
- Deleted dead duplicate CarNotificationManager / CarReplyReceiver (core already posts
  richer notifications; the car copies were never called).
- Pinned androidx.car.app 1.9.0-alpha01 → 1.7.0 stable; dropped unused app-automotive.

🛠️ Tests
- CarScreensTest: drives the real HomeScreen via TestCarContext + a CarStateCoordinator
  test seam (mokkery repos, Robolectric), asserting template-per-state and the
  ALERT_APP → emergency flow. This caught the TabTemplate crash above.
- feature/car/TESTING.md documents the verification paths.

Testing Performed: spotlessCheck, detekt, :feature🚗testGoogleDebugUnitTest (incl.
CarScreensTest), :core:service:compileAndroidMain, :androidApp:assembleGoogleDebug — all pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

…n up group summary

Replying to a message from Android Auto left the conversation showing in the head
unit, because the cancel only removed the individual notification and left the group
summary behind — and the reply never marked the conversation read.

🐛 Fixes
- cancelMessageNotification now rebuilds (or clears) the group summary, so the dismissed
  conversation doesn't linger in the Android Auto notification center.
- showGroupSummary cancels the summary entirely when no message conversations remain.
- ReplyReceiver marks the conversation read (clearUnreadCount) on reply, mirroring the
  mark-as-read action — Android Auto keys dismissal off read state.
- ReplyReceiver sends first, then dismisses in a defensive finally, so a slow/failed BLE
  send can no longer drop the reply or leave the notification stuck. Added logging.

Verified on a Pixel 6a via the Desktop Head Unit: reply sends, conversation is marked
read, and the notification (and summary) clear from the phone and the head unit.

Testing Performed: spotlessCheck, detekt, :core:service:compileAndroidMain,
:androidApp:assembleGoogleDebug — all pass; manual DHU verification on device.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>