tighten thread item + mention link spacing

Reduce vertical padding on channel feed and demo message thread items,
and trim the inline mention/link chip padding for a denser feed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: adamleithp

packages/ui/src/features/canvas/components/ChannelFeedView.tsx

@@ -403,7 +403,7 @@ const FeedItem = memo(function FeedItem({
   onOpenThread: (task: Task) => void;
 }) {
   return (
-    <ThreadItem className="rounded-none py-4 pr-8 hover:bg-fill-hover/50">
+    <ThreadItem className="rounded-none py-1 pr-8 hover:bg-fill-hover/50">
       <ThreadItemGutter>
         <Avatar>
           <AvatarFallback>
@@ -618,7 +618,7 @@ export function DemoMessageItem({
     });
   };
   return (
-    <ThreadItem className="rounded-none py-4 pr-8">
+    <ThreadItem className="rounded-none py-2 pr-8">
       <ThreadItemGutter>
         <Avatar>
           <AvatarFallback>

packages/ui/src/features/canvas/components/MentionText.tsx

@@ -102,7 +102,7 @@ export function MentionText({
   }, [content, markdownLinks]);
   const selfEmail = currentUserEmail?.toLowerCase();
   const router = useRouter();
-  const linkClass = "bg-info/50 px-1 rounded-xs";
+  const linkClass = "bg-info/50 px-0.5 rounded-xs";
   return (
     <Text size="1" className={className}>
       {segments.map(({ segment, key }) => {