feat(02-03): create task providers, form screen with frequency and effort selectors

- TaskActions AsyncNotifier for create, update, delete, complete task mutations
- tasksInRoomProvider manual StreamProvider.family wrapping TasksDao.watchTasksInRoom
- TaskFormScreen with name, frequency (10 presets + custom), effort (3-way segmented),
  description, and initial due date picker (German DD.MM.YYYY format)
- Custom frequency: number + unit picker (Tage/Wochen/Monate)
- Calendar-anchored intervals auto-set anchorDay from due date
- Edit mode loads existing task and pre-fills all fields
- 19 new German localization keys for task form, delete, and empty state

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/features/tasks/presentation/task_providers.g.dart

@@ -0,0 +1,59 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'task_providers.dart';
+
+// **************************************************************************
+// RiverpodGenerator
+// **************************************************************************
+
+// GENERATED CODE - DO NOT MODIFY BY HAND
+// ignore_for_file: type=lint, type=warning
+/// Notifier for task mutations: create, update, delete, complete.
+
+@ProviderFor(TaskActions)
+final taskActionsProvider = TaskActionsProvider._();
+
+/// Notifier for task mutations: create, update, delete, complete.
+final class TaskActionsProvider
+    extends $AsyncNotifierProvider<TaskActions, void> {
+  /// Notifier for task mutations: create, update, delete, complete.
+  TaskActionsProvider._()
+    : super(
+        from: null,
+        argument: null,
+        retry: null,
+        name: r'taskActionsProvider',
+        isAutoDispose: true,
+        dependencies: null,
+        $allTransitiveDependencies: null,
+      );
+
+  @override
+  String debugGetCreateSourceHash() => _$taskActionsHash();
+
+  @$internal
+  @override
+  TaskActions create() => TaskActions();
+}
+
+String _$taskActionsHash() => r'62f1739263e3cfb379b83de10d712b17fd087f92';
+
+/// Notifier for task mutations: create, update, delete, complete.
+
+abstract class _$TaskActions extends $AsyncNotifier<void> {
+  FutureOr<void> build();
+  @$mustCallSuper
+  @override
+  void runBuild() {
+    final ref = this.ref as $Ref<AsyncValue<void>, void>;
+    final element =
+        ref.element
+            as $ClassProviderElement<
+              AnyNotifier<AsyncValue<void>, void>,
+              AsyncValue<void>,
+              Object?,
+              Object?
+            >;
+    element.handleCreate(ref, build);
+  }
+}