feat(flutter/cache): connectivityProvider + cacheSettingsProvider

connectivityProvider — StreamProvider<bool>; true when any connectivity
result is non-none. No Wi-Fi gate per operator decision.

cacheSettingsProvider — AsyncNotifier<CacheSettings> persisting
capBytes / prefetchWindow / cacheLikedTracks via flutter_secure_storage.
Defaults: 5 GB cap, 5-track prefetch, cache liked = on.

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

flutter_client/test/cache/cache_settings_provider_test.dart

@@ -0,0 +1,76 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:mocktail/mocktail.dart';
+
+import 'package:minstrel/auth/auth_provider.dart';
+import 'package:minstrel/cache/cache_settings_provider.dart';
+
+class _MockStorage extends Mock implements FlutterSecureStorage {}
+
+void main() {
+  setUpAll(() {
+    registerFallbackValue('');
+  });
+
+  test('returns defaults when storage is empty', () async {
+    final storage = _MockStorage();
+    when(() => storage.read(key: any(named: 'key')))
+        .thenAnswer((_) async => null);
+    when(() => storage.write(
+            key: any(named: 'key'), value: any(named: 'value')))
+        .thenAnswer((_) async {});
+
+    final container = ProviderContainer(overrides: [
+      secureStorageProvider.overrideWithValue(storage),
+    ]);
+    addTearDown(container.dispose);
+
+    final s = await container.read(cacheSettingsProvider.future);
+    expect(s.capBytes, CacheSettings.defaults.capBytes);
+    expect(s.prefetchWindow, 5);
+    expect(s.cacheLikedTracks, true);
+  });
+
+  test('setPrefetchWindow clamps to 1..10', () async {
+    final storage = _MockStorage();
+    when(() => storage.read(key: any(named: 'key')))
+        .thenAnswer((_) async => null);
+    when(() => storage.write(
+            key: any(named: 'key'), value: any(named: 'value')))
+        .thenAnswer((_) async {});
+
+    final container = ProviderContainer(overrides: [
+      secureStorageProvider.overrideWithValue(storage),
+    ]);
+    addTearDown(container.dispose);
+
+    await container.read(cacheSettingsProvider.future);
+    final ctrl = container.read(cacheSettingsProvider.notifier);
+    await ctrl.setPrefetchWindow(99);
+    expect(container.read(cacheSettingsProvider).value!.prefetchWindow, 10);
+    await ctrl.setPrefetchWindow(0);
+    expect(container.read(cacheSettingsProvider).value!.prefetchWindow, 1);
+  });
+
+  test('setCacheLikedTracks toggles persisted', () async {
+    final storage = _MockStorage();
+    when(() => storage.read(key: any(named: 'key')))
+        .thenAnswer((_) async => null);
+    when(() => storage.write(
+            key: any(named: 'key'), value: any(named: 'value')))
+        .thenAnswer((_) async {});
+
+    final container = ProviderContainer(overrides: [
+      secureStorageProvider.overrideWithValue(storage),
+    ]);
+    addTearDown(container.dispose);
+
+    await container.read(cacheSettingsProvider.future);
+    await container.read(cacheSettingsProvider.notifier).setCacheLikedTracks(false);
+    expect(
+        container.read(cacheSettingsProvider).value!.cacheLikedTracks, false);
+    verify(() => storage.write(key: 'cache_liked_tracks', value: 'false'))
+        .called(1);
+  });
+}

flutter_client/test/cache/connectivity_provider_test.dart

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+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:minstrel/cache/connectivity_provider.dart';
+
+void main() {
+  test('connectivityProvider is reachable from a ProviderContainer', () {
+    // Smoke test: provider builds without throwing. Real connectivity
+    // tests would need a connectivity_plus mock; defer to manual ops.
+    final container = ProviderContainer();
+    addTearDown(container.dispose);
+    expect(container.read(connectivityProvider.future), isA<Future<bool>>());
+  });
+}