style(headlines-search): update TODO comments and improve code consistency

- Replace generic 'user' with my username 'fulleni' in TODO comments
- Improve consistency of TODO comment formatting
- Remove unnecessary comments related to content type filtering
- Adjust comments about localization to reflect current implementation status

Author: fulleni

lib/headlines-search/view/headlines_search_page.dart

@@ -56,7 +56,7 @@ class _HeadlinesSearchViewState extends State<_HeadlinesSearchView> {
         _showClearButton = _textController.text.isNotEmpty;
       });
     });
-    // TODO(user): This logic might need adjustment if not all ContentType values are searchable.
+    // TODO(fulleni): This logic might need adjustment if not all ContentType values are searchable.
     // For now, we default to headline if the current selection is not in the allowed list.
     final searchableTypes = [
       ContentType.headline,
@@ -110,7 +110,7 @@ class _HeadlinesSearchViewState extends State<_HeadlinesSearchView> {
     final textTheme = theme.textTheme;
     final appBarTheme = theme.appBarTheme;
 
-    // TODO(user): Replace this with a filtered list of searchable content types.
+    // TODO(fulleni): Replace this with a filtered list of searchable content types.
     final availableSearchModelTypes = [
       ContentType.headline,
       ContentType.topic,
@@ -159,7 +159,7 @@ class _HeadlinesSearchViewState extends State<_HeadlinesSearchView> {
                       appBarTheme.iconTheme?.color ??
                       colorScheme.onSurfaceVariant,
                 ),
-                // TODO(user): Use the new localization extension here.
+                // TODO(fulleni): Use the new localization extension here.
                 items: availableSearchModelTypes.map((ContentType type) {
                   return DropdownMenuItem<ContentType>(
                     value: type,
@@ -187,7 +187,7 @@ class _HeadlinesSearchViewState extends State<_HeadlinesSearchView> {
                 controller: _textController,
                 style: appBarTheme.titleTextStyle ?? textTheme.titleMedium,
                 decoration: InputDecoration(
-                  // TODO(user): Create a similar localization extension for hint text.
+                  // TODO(fulleni): Create a similar localization extension for hint text.
                   hintText: 'Search...',
                   hintStyle: textTheme.bodyMedium?.copyWith(
                     color: