refactor: extract notification tap routing into its own file

Legacy handled tap → navigation inside notify.dart; the rewrite had it
as a private method on the app service host. Move it to
notification_routes.dart (which already owns the channel → route table)
as routeNotificationTap — the app host just registers it on
NotificationTaps — with an injectable navigate for tests.

Author: whes1015

lib/app/app.dart

@@ -6,7 +6,6 @@ import 'package:dpip/core/geo/device_location_reporter.dart';
 import 'package:dpip/core/geo/location_monitor.dart';
 import 'package:dpip/core/geo/location_service.dart';
 import 'package:dpip/core/notifications/notification_service.dart';
-import 'package:dpip/core/notifications/notification_tap.dart';
 import 'package:dpip/core/notifications/notification_taps.dart';
 import 'package:dpip/core/platform/background_location.dart';
 import 'package:dpip/core/realtime/realtime_lifecycle.dart';
@@ -75,8 +74,8 @@ class DpipApp extends StatelessWidget {
 
 /// Owns app-level service wiring that needs a [State]/lifecycle:
 /// - the realtime spine's start/pause/resume (via [RealtimeLifecycleObserver]);
-/// - routing a tapped notification to the right tab (the channel-key → route
-///   mapping lives here because this layer owns the router);
+/// - registering the notification tap → route handler ([routeNotificationTap],
+///   whose channel→screen table lives in `notification_routes.dart`);
 /// - requesting notification permission once, after the first frame;
 /// - resolving the current GPS township into the [RegionStore] so 所在地 shows
 ///   the real location (and the "can't get location" state when GPS is off).
@@ -117,7 +116,7 @@ class _AppServicesHostState extends State<_AppServicesHost>
     super.initState();
     _observer = RealtimeLifecycleObserver(widget.realtimeService);
     WidgetsBinding.instance.addObserver(this);
-    NotificationTaps.onTap = _routeNotificationTap;
+    NotificationTaps.onTap = routeNotificationTap;
     widget.onboarding.addListener(_onOnboardingChanged);
     WidgetsBinding.instance.addPostFrameCallback((_) {
       widget.realtimeService.startAll();
@@ -188,13 +187,6 @@ class _AppServicesHostState extends State<_AppServicesHost>
     super.dispose();
   }
 
-  /// Sends a tapped notification to a screen. The destination is resolved by the
-  /// declarative channel→route table; the tap's [NotificationTap.id] is carried
-  /// for the per-item detail routes to come.
-  void _routeNotificationTap(NotificationTap tap) {
-    appRouter.goNamed(routeForNotificationChannel(tap.channelKey));
-  }
-
   @override
   Widget build(BuildContext context) => widget.child;
 }

lib/app/router/notification_routes.dart

@@ -1,7 +1,35 @@
+import 'package:dpip/app/router/app_router.dart';
 import 'package:dpip/core/logging/log.dart';
 import 'package:dpip/core/notifications/notification_channels.dart';
+import 'package:dpip/core/notifications/notification_tap.dart';
 import 'package:dpip/shared/navigation/app_routes.dart';
 
+/// The slice of the router a notification tap needs — [GoRouter.goNamed].
+typedef NotificationRouteNavigator = void Function(
+  String name, {
+  Map<String, String> pathParameters,
+  Map<String, dynamic> queryParameters,
+  String? fragment,
+  Object? extra,
+});
+
+/// Single owner of notification → destination, mirroring the legacy
+/// `notify.dart` tap table in one file: [NotificationTaps] carries the tap
+/// intent and calls [routeNotificationTap] once the router is live (replaying a
+/// cold-start tap through [NotificationTaps.drainPending]). The channel
+/// resolves to a route name via the declarative group table below, then the
+/// router navigates — no widget hosts this logic, so adding an alert family is
+/// one row in the table and nothing else.
+///
+/// [navigate] is injectable for tests; it defaults to the app router's
+/// [GoRouter.goNamed].
+void routeNotificationTap(
+  NotificationTap tap, {
+  NotificationRouteNavigator? navigate,
+}) {
+  (navigate ?? appRouter.goNamed)(routeForNotificationChannel(tap.channelKey));
+}
+
 /// Resolves a tapped notification's channel to a destination route.
 ///
 /// Declarative and group-driven (via [NotificationChannels.groupOf]) instead of

test/app/router/notification_routes_test.dart

@@ -1,5 +1,6 @@
 import 'package:dpip/app/router/notification_routes.dart';
 import 'package:dpip/core/notifications/notification_channels.dart';
+import 'package:dpip/core/notifications/notification_tap.dart';
 import 'package:dpip/shared/navigation/app_routes.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -70,4 +71,39 @@ void main() {
     expect(routeForNotificationChannel('does-not-exist'), AppRoutes.home);
     expect(routeForNotificationChannel(null), AppRoutes.home);
   });
+
+  test('routeNotificationTap navigates to the resolved route', () {
+    final named = <String>[];
+    void record(
+      String name, {
+      Map<String, String> pathParameters = const {},
+      Map<String, dynamic> queryParameters = const {},
+      String? fragment,
+      Object? extra,
+    }) {
+      named.add(name);
+    }
+
+    // EEW channel → the live monitor tab.
+    routeNotificationTap(
+      const NotificationTap(channelKey: 'eew_alert-important-v2'),
+      navigate: record,
+    );
+    // Report family → the report list tab.
+    routeNotificationTap(
+      const NotificationTap(channelKey: 'report-general-v2'),
+      navigate: record,
+    );
+    // An unmapped channel falls back to home rather than throwing.
+    routeNotificationTap(
+      const NotificationTap(channelKey: 'does-not-exist'),
+      navigate: record,
+    );
+
+    expect(named, [
+      AppRoutes.eew,
+      AppRoutes.earthquake,
+      AppRoutes.home,
+    ]);
+  });
 }