fix(app): preventDefault in capture phase for MarkdownLink anchor

Pressable's click handler calls stopPropagation, so the bubble-phase
preventDefault on the wrapping <a> never fired and the Electron view
navigated to the href in addition to the existing helper opening it
in the OS browser. Move preventDefault to onClickCapture (and
onAuxClickCapture for middle-click) so it always runs first. The
existing Pressable.onPress helper remains the only path that actually
opens links.

packages/app/src/components/message.tsx

@@ -908,7 +908,12 @@ function MarkdownLink({
   }
 
   return (
-    <a href={href} onClick={preventAnchorNavigation} style={MARKDOWN_LINK_ANCHOR_STYLE}>
+    <a
+      href={href}
+      onClickCapture={preventAnchorNavigation}
+      onAuxClickCapture={preventAnchorNavigation}
+      style={MARKDOWN_LINK_ANCHOR_STYLE}
+    >
       <Pressable
         accessibilityRole="link"
         onPress={handlePress}