Phase 3 testing fixes: Fastify 5, SSE→WebSocket+FCM, enums, security, session lifecycle

- Upgrade Fastify 4→5 with all plugins (@fastify/websocket 11, cors 11, sensible 6)
- Migrate all SSE endpoints to WebSocket + FCM push (mitra chat requests, customer pairing status)
- Add flutter_local_notifications for foreground push notifications with sound
- Add splash screen to both apps (hide auth loading flash)
- Introduce constants/enums across entire codebase (no raw string literals)
- Move price tiers from hardcoded array to app_config DB (data-driven, includes 1-min test tier)
- Add session ownership validation on all shared chat routes
- Add ownership checks on endSession, respondToExtension, requestExtension
- Fix session timer: auto-complete expired/stale sessions on server restart
- Add 5-min grace period for abandoned closing sessions
- Fix extension flow: proper session_resumed handling, clearExtensionRequest, closure grace timer cleanup
- Fix chat screens: ConnectChat in initState, session status check on connect
- Fix customer expired view: 5-min countdown, closure state priority over expired state
- Fix mitra extension UI: loading spinner, disable buttons, handle EXTENSION_RESOLVED error
- Fix GoRouter navigation consistency (no more Navigator.pushNamed)
- Fix goodbye view keyboard overflow (SingleChildScrollView)
- Add active session card on customer home screen with refresh on navigate back
- Fix PricingBottomSheet extension mode (RequestExtension instead of new pairing)
- Send session_resumed to both parties on extension accept

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

mitra_app/lib/features/chat/screens/active_sessions_screen.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:go_router/go_router.dart';
 import '../../../core/api/api_client.dart';
 
 class ActiveSessionsScreen extends StatefulWidget {
@@ -72,14 +73,19 @@ class _ActiveSessionsScreenState extends State<ActiveSessionsScreen> {
                   itemCount: _sessions.length,
                   itemBuilder: (context, index) {
                     final session = _sessions[index];
+                    final customerName = session['customer_display_name'] as String? ?? 'Customer';
                     return ListTile(
-                      leading: const Icon(Icons.person),
-                      title: Text(session['customer_display_name'] as String? ?? 'Customer'),
+                      leading: const Icon(Icons.chat),
+                      title: Text(customerName),
                       subtitle: Text('Status: ${session['status']}'),
                       trailing: TextButton(
                         onPressed: () => _endSession(session['id'] as String),
                         child: const Text('Akhiri', style: TextStyle(color: Colors.red)),
                       ),
+                      onTap: () => context.push(
+                        '/chat/session/${session['id']}',
+                        extra: {'customerName': customerName},
+                      ),
                     );
                   },
                 ),