V3-12: crash reporting (code only)

shouldInitializeCrashReporting() and scrubExtra() are pure, fully unit-tested decision/scrubbing functions wired into sentry_flutter via beforeSend/beforeBreadcrumb. Config.crashReportingEnabled defaults off; the DSN is a compile-time --dart-define, not a preference. RecordingEngine gained an injected onUnexpectedStop callback, firing once when restoreAfterProcessDeath finds a trip still 'recording' at launch -- the process died without a user stop.

Marked partially done: the ticket's real acceptance criteria (a forced crash landing in a real Sentry project from a release build, inspecting a real payload) need a Sentry account and a release build this environment can't produce.

lib/src/app/providers.dart

@@ -14,6 +14,7 @@ import '../config/config.dart';
 import '../data/database.dart';
 import '../data/trip_repository.dart';
 import '../domain/models.dart';
+import '../crash/crash_reporter.dart';
 import '../data/route_plan_repository.dart';
 import '../notification/ride_notification_controller.dart';
 import '../notification/ride_notification_coordinator.dart';
@@ -69,6 +70,8 @@ final recordingEngineProvider = Provider<RecordingEngine>((ref) {
     repository: ref.watch(tripRepositoryProvider),
     locationSource: ref.watch(locationSourceProvider),
     uploadPending: () async => ref.read(uploaderProvider)?.uploadPending(),
+    onUnexpectedStop: (reason) =>
+        reportUnexpectedRecordingStop(reason: reason),
   );
   ref.onDispose(engine.dispose);
   return engine;
@@ -120,6 +123,14 @@ final mountedModeProvider = StateProvider<bool>(
   (ref) => ref.watch(configProvider)?.mountedMode ?? false,
 );
 
+/// V3-12: same shape again. Note that flipping this at runtime does not retroactively
+/// start or stop a Sentry client already initialised at app launch -- see
+/// `maybeInitCrashReporting`'s doc comment on why that gate is checked once, in
+/// `main()`, not read reactively.
+final crashReportingEnabledProvider = StateProvider<bool>(
+  (ref) => ref.watch(configProvider)?.crashReportingEnabled ?? false,
+);
+
 /// Overridden in tests with [FakeWakelockController].
 final wakelockControllerProvider = Provider<WakelockController>(
   (ref) => PlusWakelockController(),