fix: resolve all dart analyze warnings

- Migrate RadioListTile to RadioGroup API (Flutter 3.32+)
- Guard BuildContext usage across async gaps
- Use const BorderRadius.all / EdgeInsets.all constructors
- Extract nested ternaries into helpers
- Prefer .first over [0], ??= over if-null assignment
- Prefix unused FocusNode params with _
- Add library directive for dangling doc comments

lib/widgets/focusable_list_tile.dart

@@ -116,7 +116,7 @@ class _FocusableListTileState extends State<FocusableListTile> {
 /// A RadioListTile that accepts a FocusNode for keyboard/controller navigation.
 ///
 /// Uses Flutter's native RadioListTile focus support - no custom styling wrapper.
-/// Can be used standalone with [groupValue]/[onChanged] or inside a [RadioGroup].
+/// Requires a [RadioGroup] ancestor to manage selection state.
 class FocusableRadioListTile<T> extends StatelessWidget {
   /// The primary content of the list tile.
   final Widget? title;
@@ -130,14 +130,6 @@ class FocusableRadioListTile<T> extends StatelessWidget {
   /// The value represented by this radio button.
   final T value;
 
-  /// The currently selected value for the group.
-  /// When provided, the widget works without a [RadioGroup] ancestor.
-  final T? groupValue;
-
-  /// Called when this radio button is selected.
-  /// When provided, the widget works without a [RadioGroup] ancestor.
-  final ValueChanged<T?>? onChanged;
-
   /// Whether this radio button is part of a vertically dense list.
   final bool dense;
 
@@ -156,8 +148,6 @@ class FocusableRadioListTile<T> extends StatelessWidget {
     this.subtitle,
     this.secondary,
     required this.value,
-    this.groupValue,
-    this.onChanged,
     this.dense = false,
     this.focusNode,
     this.autofocus = false,
@@ -171,8 +161,6 @@ class FocusableRadioListTile<T> extends StatelessWidget {
       subtitle: subtitle,
       secondary: secondary,
       value: value,
-      groupValue: groupValue,
-      onChanged: onChanged,
       dense: dense,
       focusNode: focusNode,
       autofocus: autofocus,