style(blog): smaller list headers, readable date color

list-view post titles were h3 at the bootstrap default, large enough
to wrap; size them to 1.4rem. dates used bootstrap's text-muted, whose
dark grey contrasts poorly on the dark background — replace with a
blog-date class matching the site's opacity-based muted-text pattern,
on the list and the detail page.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/src/App.css

@@ -191,6 +191,15 @@ a.hot-pink {
   overflow-x: auto;
 }
 
+.blog-list-title {
+  font-size: 1.4rem;
+}
+
+.blog-date {
+  font-size: 85%;
+  opacity: 0.6;
+}
+
 .site-footer {
   margin-top: 3rem;
   padding: 1rem 0;