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/main.dart

@@ -1,5 +1,11 @@
-// Version: 1.2.0 | Created: 2026-04-01 | Updated: 2026-04-27
+// Version: 1.3.0 | Created: 2026-04-01 | Updated: 2026-09-25
 // Application entry point.
+// v1.3.0: wires SessionJourney (session/journey/friction tracking, ported
+// from the WordPress sites per plan ancient-petting-hejlsberg.md §3/§5).
+// WidgetsFlutterBinding.ensureInitialized() stays the literal first line —
+// calling SessionJourney.init() before it crashes the release web build
+// with a null-check error (found and fixed on GardenBuddy the same day,
+// 2026-09-25 — not repeating that mistake here).
 
 import 'dart:async';
 
@@ -9,6 +15,7 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:olm/olm.dart' as olm;
 
 import 'app/app.dart';
+import 'core/analytics/session_journey.dart';
 import 'core/push/web_push_service.dart';
 
 void main() async {
@@ -17,7 +24,9 @@ void main() async {
   // Check Olm availability — this prints to the browser console.
   try {
     await olm.init();
-    debugPrint('[M8Chat] Olm initialized successfully: ${olm.get_library_version()}');
+    debugPrint(
+      '[M8Chat] Olm initialized successfully: ${olm.get_library_version()}',
+    );
   } catch (e) {
     debugPrint('[M8Chat] Olm NOT available: $e');
   }
@@ -41,5 +50,10 @@ void main() async {
     return true; // returning true marks the error as handled
   };
 
+  // SessionJourney.init() runs AFTER the two handlers above so it CHAINS to
+  // them (captures them as "previous", calls them after its own reporting)
+  // rather than replacing them. See session_journey.dart's header.
+  SessionJourney.init(appVersion: '1.12.0');
+
   runApp(const ProviderScope(child: M8ChatApp()));
 }