Phase 3.1 WIP: Riverpod migration (client_app Auth + ChatOpening)

- Add phase3.1 requirement and implementation plan docs
- Add Riverpod dependencies to both client_app and mitra_app
- Wrap both app roots with ProviderScope
- Migrate client_app AuthBloc → AuthNotifier (@riverpod annotation)
- Migrate client_app ChatOpeningBloc → chatPricingProvider (FutureProvider)
- Update router to use Riverpod-based auth state for redirects
- Update all auth screens (display name, register, OTP, force register)
- Update home screen and pricing bottom sheet
- Add android:usesCleartextTraffic for dev HTTP access on both apps
- mitra_app prepared with ProviderScope + ApiClient provider (blocs next)

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

mitra_app/lib/core/api/api_client_provider.dart

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+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+import 'api_client.dart';
+
+part 'api_client_provider.g.dart';
+
+@Riverpod(keepAlive: true)
+ApiClient apiClient(Ref ref) => ApiClient();

mitra_app/lib/core/api/api_client_provider.g.dart

@@ -0,0 +1,26 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'api_client_provider.dart';
+
+// **************************************************************************
+// RiverpodGenerator
+// **************************************************************************
+
+String _$apiClientHash() => r'90c807f03b90249684265cc91739139c2c89eeb9';
+
+/// See also [apiClient].
+@ProviderFor(apiClient)
+final apiClientProvider = Provider<ApiClient>.internal(
+  apiClient,
+  name: r'apiClientProvider',
+  debugGetCreateSourceHash:
+      const bool.fromEnvironment('dart.vm.product') ? null : _$apiClientHash,
+  dependencies: null,
+  allTransitiveDependencies: null,
+);
+
+@Deprecated('Will be removed in 3.0. Use Ref instead')
+// ignore: unused_element
+typedef ApiClientRef = ProviderRef<ApiClient>;
+// ignore_for_file: type=lint
+// ignore_for_file: subtype_of_sealed_class, invalid_use_of_internal_member, invalid_use_of_visible_for_testing_member, deprecated_member_use_from_same_package