fix: resolve all flutter analyze warnings and infos

- app.dart: add braces to single-statement if body
- briefing_api.dart: escape <id> in doc comment (unintended HTML)
- notes_api.dart, tasks_api.dart, projects_api.dart: use null-aware
  map elements (?'key': value) instead of if-null guards
- task_edit_screen.dart: remove unused tasks_api.dart import
- task_edit_screen.dart, project_selector.dart: suppress
  deprecated_member_use on DropdownButtonFormField.value (value is
  the controlled-widget param; switching to initialValue would break
  current-selection display)
- project_selector.dart: use _ instead of __ for ignored error params

lib/screens/tasks/task_edit_screen.dart

@@ -4,7 +4,6 @@ import 'package:go_router/go_router.dart';
 
 import '../../core/constants.dart';
 import '../../core/exceptions.dart';
-import '../../data/api/tasks_api.dart';
 import '../../data/models/task.dart';
 import '../../providers/api_client_provider.dart';
 import '../../providers/tasks_provider.dart';
@@ -239,6 +238,7 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
                           ),
                           const SizedBox(height: 16),
                           DropdownButtonFormField<TaskStatus>(
+                            // ignore: deprecated_member_use
                             value: _status,
                             decoration: const InputDecoration(
                               labelText: 'Status',
@@ -253,6 +253,7 @@ class _TaskEditScreenState extends ConsumerState<TaskEditScreen> {
                           ),
                           const SizedBox(height: 16),
                           DropdownButtonFormField<TaskPriority>(
+                            // ignore: deprecated_member_use
                             value: _priority,
                             decoration: const InputDecoration(
                               labelText: 'Priority',