Phase 3.4: mitra_app self-managed auth cutover

Rips firebase_auth; phone OTP flow now talks directly to the new
backend endpoints, JWT access token lives in memory, refresh token
persists via flutter_secure_storage. WebSocket handshakes read the
access token from AuthBridge instead of Firebase.

Smoke-tested end-to-end against the backend via curl:
- otp/request → read stub code from backend log → otp/verify
- /api/mitra/auth/me + /api/shared/auth/refresh rotation
- logout → post-logout refresh correctly fails REFRESH_INVALID
- ACCOUNT_INACTIVE (403) + WRONG_FLOW (400) error paths verified
- Debug APK links cleanly

- pubspec: drop firebase_auth, add flutter_secure_storage
- core/auth/auth_bridge.dart: shared mutable state (access token +
  refresh callback + in-flight de-dup) as keepAlive provider
- core/auth/token_storage.dart: flutter_secure_storage wrapper
- core/auth/auth_notifier.dart: bootstrap → refresh; requestOtp +
  verifyOtp via /api/mitra/auth/*; logout; granular OTP error codes
- core/api/api_client.dart: Bearer from bridge + postRaw(skipAuth) for
  auth endpoints + single-retry 401 refresh
- core/chat/*_notifier.dart: WS auth frame reads bridge.accessToken
- features/auth/screens/otp_screen.dart: verificationId → otpRequestId
- mitra_app/CLAUDE.md: Auth section rewritten (was stale on Firebase)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mitra_app/lib/core/chat/chat_request_notifier.dart

@@ -1,11 +1,11 @@
 import 'dart:async';
 import 'dart:convert';
 import 'package:dio/dio.dart';
-import 'package:firebase_auth/firebase_auth.dart';
 import 'package:riverpod_annotation/riverpod_annotation.dart';
 import 'package:web_socket_channel/web_socket_channel.dart';
 import '../api/api_client.dart';
 import '../api/api_client_provider.dart';
+import '../auth/auth_bridge.dart';
 import '../constants.dart';
 import '../notifications/notification_service.dart';
 
@@ -147,10 +147,9 @@ class ChatRequest extends _$ChatRequest {
 
   Future<void> _connectWebSocket() async {
     try {
-      final user = FirebaseAuth.instance.currentUser;
-      if (user == null) return;
+      final token = ref.read(authBridgeProvider).accessToken;
+      if (token == null) return;
 
-      final token = await user.getIdToken();
       final wsUrl = ApiClient.baseUrl
           .replaceFirst('https://', 'wss://')
           .replaceFirst('http://', 'ws://');

mitra_app/lib/core/chat/chat_request_notifier.g.dart

@@ -6,7 +6,7 @@ part of 'chat_request_notifier.dart';
 // RiverpodGenerator
 // **************************************************************************
 
-String _$chatRequestHash() => r'c80b16e371658fbbaca88a75b48e16a3c0e057b3';
+String _$chatRequestHash() => r'52aeaca594a44be3eeef7d264a1f311004b38416';
 
 /// See also [ChatRequest].
 @ProviderFor(ChatRequest)

mitra_app/lib/core/chat/extension_notifier.g.dart

@@ -6,7 +6,7 @@ part of 'extension_notifier.dart';
 // RiverpodGenerator
 // **************************************************************************
 
-String _$mitraExtensionHash() => r'4eed73b51454238e2cd40a255c148f232f281913';
+String _$mitraExtensionHash() => r'e1346601df43c42aea6f2bc984b507547507a57c';
 
 /// See also [MitraExtension].
 @ProviderFor(MitraExtension)

mitra_app/lib/core/chat/mitra_chat_notifier.dart

@@ -1,11 +1,11 @@
 import 'dart:async';
 import 'dart:convert';
 import 'package:dio/dio.dart';
-import 'package:firebase_auth/firebase_auth.dart';
 import 'package:riverpod_annotation/riverpod_annotation.dart';
 import 'package:web_socket_channel/web_socket_channel.dart';
 import '../api/api_client.dart';
 import '../api/api_client_provider.dart';
+import '../auth/auth_bridge.dart';
 import '../constants.dart';
 
 part 'mitra_chat_notifier.g.dart';
@@ -137,8 +137,11 @@ class MitraChat extends _$MitraChat {
         createdAt: DateTime.parse(m['created_at'] as String),
       )).toList();
 
-      final user = FirebaseAuth.instance.currentUser;
-      final token = await user?.getIdToken();
+      final token = ref.read(authBridgeProvider).accessToken;
+      if (token == null) {
+        state = const MitraChatErrorData('Sesi berakhir. Silakan login ulang.');
+        return;
+      }
       final wsUrl = ApiClient.baseUrl
           .replaceFirst('https://', 'wss://')
           .replaceFirst('http://', 'ws://');

mitra_app/lib/core/chat/mitra_chat_notifier.g.dart

@@ -6,7 +6,7 @@ part of 'mitra_chat_notifier.dart';
 // RiverpodGenerator
 // **************************************************************************
 
-String _$mitraChatHash() => r'827aa874dbcf49c17f94c0507f5e0a4064bcede3';
+String _$mitraChatHash() => r'd5f4819264b9c71ce29a640ee2cfee608ead5e9e';
 
 /// See also [MitraChat].
 @ProviderFor(MitraChat)