extract ClideTappable shared widget

Encapsulates the hover + click + cursor pattern repeated across
the codebase. Builder receives (context, hovered) so callers
control their own hover styling. Refactored _ThemeLink to use it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/widgets/src/clide_tappable.dart

@@ -0,0 +1,35 @@
+import 'package:flutter/widgets.dart';
+
+class ClideTappable extends StatefulWidget {
+  const ClideTappable({
+    super.key,
+    required this.onTap,
+    required this.builder,
+    this.cursor = SystemMouseCursors.click,
+  });
+
+  final VoidCallback onTap;
+  final Widget Function(BuildContext context, bool hovered) builder;
+  final MouseCursor cursor;
+
+  @override
+  State<ClideTappable> createState() => _ClideTappableState();
+}
+
+class _ClideTappableState extends State<ClideTappable> {
+  bool _hover = false;
+
+  @override
+  Widget build(BuildContext context) {
+    return MouseRegion(
+      cursor: widget.cursor,
+      onEnter: (_) => setState(() => _hover = true),
+      onExit: (_) => setState(() => _hover = false),
+      child: GestureDetector(
+        behavior: HitTestBehavior.opaque,
+        onTap: widget.onTap,
+        child: widget.builder(context, _hover),
+      ),
+    );
+  }
+}