feat: render desktop latest section as 3-column masonry

- Matches Figma design (file uHDZkVHjAp7BXDKQKB0PM4, node 4367-11405).
- Mobile keeps the existing 5-post single column unchanged.
- Desktop (md+) renders all 12 latest posts in a CSS-columns masonry
  with break-inside-avoid so each card's height stays content-driven.
- Adds an optional 'fluid' prop to MessageBubble that drops the
  standalone-feed max-widths so bubbles fill the masonry column. The
  /browse stream keeps the default non-fluid widths.

src/pages/Home/index.tsx

@@ -464,13 +464,25 @@ export function Home() {
                 viewAllLabel={t("viewAll")}
               />
             </div>
-            <div className="mt-2.5 flex flex-col gap-3 md:mt-7">
+            <div className="mt-2.5 flex flex-col gap-3 md:hidden">
               {latestPosts.slice(0, 5).map((post, index) => (
                 <Reveal key={post.id} delay={Math.min(index, 8) * 0.05}>
                   <MessageBubble post={post} />
                 </Reveal>
               ))}
             </div>
+            {/* Desktop: 3-column masonry that matches the Figma layout. */}
+            <div className="mt-7 hidden gap-4 md:block md:columns-3">
+              {latestPosts.map((post, index) => (
+                <Reveal
+                  key={post.id}
+                  delay={Math.min(index, 8) * 0.05}
+                  className="mb-4 break-inside-avoid"
+                >
+                  <MessageBubble post={post} fluid />
+                </Reveal>
+              ))}
+            </div>
           </div>
         </section>
       </Reveal>