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/widgets/project_selector.dart

@@ -23,12 +23,13 @@ class ProjectSelector extends ConsumerWidget {
 
     return projectsAsync.when(
       loading: () => const LinearProgressIndicator(),
-      error: (_, __) => const SizedBox.shrink(),
+      error: (_, _) => const SizedBox.shrink(),
       data: (projects) {
         final active =
             projects.where((p) => p.status == 'active').toList();
 
         return DropdownButtonFormField<int?>(
+          // ignore: deprecated_member_use
           value: value,
           decoration: decoration ??
               const InputDecoration(