Show topics on the home page, name the current one in the header

The home page fell back to PaperMod's recursive page list, which dumped
digest pages instead of the research topics they belong to. Add a home
layout that renders one card per entry in data/topics.yaml, with venue
counts, the nearest upcoming deadline, and section shortcuts.

With the topics listed there, drop the topic menu from the header and
show the current topic beside the site title instead, so the selected
research area is visible from every page. The breadcrumbs then repeated
that prefix, so override the partial to start below the topic section.

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

site/assets/css/extended/custom.css

@@ -15,6 +15,47 @@
     }
 }
 
+/* Current topic shown beside the site title. PaperMod's .logo a carries the
+   full title weight; the topic reads as a secondary breadcrumb. */
+.logo-sep {
+    margin: 0 6px;
+    color: var(--secondary);
+    font-size: 24px;
+    font-weight: 400;
+}
+
+.logo .logo-topic {
+    font-size: 24px;
+    font-weight: 500;
+    color: var(--secondary);
+}
+
+/* Topic cards on the home page. The stats line and the section shortcuts sit
+   inside PaperMod's .post-entry, whose ::before overlay swallows clicks, so the
+   shortcut links need to be lifted above it to stay clickable. */
+.topic-stats {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 4px 16px;
+    margin: 8px 0 0;
+    padding: 0;
+    list-style: none;
+    font-size: 14px;
+    color: var(--secondary);
+}
+
+.topic-links {
+    display: flex;
+    gap: 16px;
+    margin-top: 10px;
+    position: relative;
+    z-index: 1;
+}
+
+.topic-links a {
+    box-shadow: 0 1px 0 var(--primary);
+}
+
 /* Intro copy above a list of cards. PaperMod gives .post-entry a bottom margin
    only, and .md-content zeroes its last child's, so the intro would otherwise
    sit flush against the first card. Matches the card-to-card gap. */