simplified code across the app and consolidated duplicated helpers

lib/view/pages/talk/widgets/highlighted_linkify.dart

@@ -62,14 +62,12 @@ class HighlightedLinkify extends StatefulWidget {
   final String? highlight;
   final LinkCallback? onOpen;
   final TextStyle? style;
-  final TextStyle? linkStyle;
 
   const HighlightedLinkify({
     required this.text,
     this.highlight,
     this.onOpen,
     this.style,
-    this.linkStyle,
     super.key,
   });
 
@@ -126,11 +124,7 @@ class _HighlightedLinkifyState extends State<HighlightedLinkify> {
     // drops link color/underline because TextStyle.merge treats explicit
     // nulls in the overlay as "leave unchanged".
     final linkStyle = defaultStyle.merge(
-      widget.linkStyle ??
-          const TextStyle(
-            color: Colors.blue,
-            decoration: TextDecoration.underline,
-          ),
+      const TextStyle(color: Colors.blue, decoration: TextDecoration.underline),
     );
     const linkHighlight = TextStyle(
       backgroundColor: Color(0xFFFFD54F),