feat(analytics): port SessionJourney tracking from GardenBuddy (v1.12.0+16)

Rolls the session/journey/friction tracking module out to M8Chat app2, per
plan ancient-petting-hejlsberg.md §5 step 4. Same pattern as GardenBuddy's
same-day port: SessionJourney.init() wired after WidgetsFlutterBinding.
ensureInitialized() and after the existing FlutterError.onError /
PlatformDispatcher.instance.onError handlers, which it chains rather than
replaces. SessionJourneyNavigatorObserver registered on the GoRouter
instance; SessionJourneyGestureLayer wraps MaterialApp.router for rage-tap
detection.

This repo has no shared offline-cache module like GardenBuddy's
core/offline/, so persistence is a small scoped sj_local_store.dart using
the package:web dependency already present in the repo (localStorage on
web, in-memory fallback for the test VM), rather than adding a new package.

app_key m8chat.au-app was reserved today in track.php v2.0.1's
allowed_sites/allowed_origins for https://app2.m8chat.au, confirmed by grep
before use.

Verified live: build deployed to app2.m8chat.au (md5-matched), Playwright
navigation produced real session/visitor/screen_view rows in
admin_flutterstats with app_key=m8chat.au-app, nginx logs show no 5xx and
no real visitor served a broken build during the test window.

lib/app/app.dart

@@ -1,11 +1,16 @@
-// Version: 1.1.0 | Created: 2026-04-01 | Updated: 2026-07-04
+// Version: 1.2.0 | Created: 2026-04-01 | Updated: 2026-09-25
 // Root MaterialApp widget. Wires together theme + router + incoming-call
 // overlay (v1.1.0 — the overlay existed but was never mounted, so incoming
 // calls showed nothing).
+// v1.2.0: wrapped in SessionJourneyGestureLayer for rage-tap detection
+// (plan ancient-petting-hejlsberg.md §3/§5). Placed above MaterialApp.router
+// so it sees every PointerDownEvent in the tree without competing for
+// gesture-arena ownership with in-app gestures.
 
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
+import '../core/analytics/session_journey.dart';
 import '../features/calls/presentation/incoming_call_overlay.dart';
 import 'router.dart';
 import 'theme.dart';
@@ -21,16 +26,18 @@ class M8ChatApp extends ConsumerWidget {
   Widget build(BuildContext context, WidgetRef ref) {
     final router = ref.watch(routerProvider);
 
-    return MaterialApp.router(
-      title: 'M8Chat',
-      theme: buildLightTheme(),
-      darkTheme: buildDarkTheme(),
-      // Default to dark — M8Chat is a dark-first chat app.
-      themeMode: ThemeMode.system,
-      routerConfig: router,
-      debugShowCheckedModeBanner: false,
-      builder: (context, child) =>
-          IncomingCallOverlayHost(child: child ?? const SizedBox.shrink()),
+    return SessionJourneyGestureLayer(
+      child: MaterialApp.router(
+        title: 'M8Chat',
+        theme: buildLightTheme(),
+        darkTheme: buildDarkTheme(),
+        // Default to dark — M8Chat is a dark-first chat app.
+        themeMode: ThemeMode.system,
+        routerConfig: router,
+        debugShowCheckedModeBanner: false,
+        builder: (context, child) =>
+            IncomingCallOverlayHost(child: child ?? const SizedBox.shrink()),
+      ),
     );
   }
 }