fix(home): focus-visible auf section-head + scoped chev-CSS

Code-Review zu commit 2216c89: button hatte keinen :focus-visible
Outline (Safari zeigt sonst gar nichts an) — Pattern aus dem Rest
der Page uebernommen (#2b6a3d Outline). Globale .chev-Selektoren
unter .section-head gescoped, damit andere Komponenten den Klassen-
Namen kuenftig wiederverwenden koennen ohne Konflikte.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/routes/+page.svelte

@@ -624,6 +624,10 @@
   .section-head:hover {
     background: #f4f8f5;
   }
+  .section-head:focus-visible {
+    outline: 2px solid #2b6a3d;
+    outline-offset: 2px;
+  }
   .section-head h2 {
     margin: 0;
     font-size: 1.05rem;
@@ -636,12 +640,12 @@
     font-size: 0.85rem;
     font-variant-numeric: tabular-nums;
   }
-  :global(.chev) {
+  .section-head :global(.chev) {
     color: #2b6a3d;
     flex-shrink: 0;
     transition: transform 180ms;
   }
-  :global(.chev.rotated) {
+  .section-head :global(.chev.rotated) {
     transform: rotate(-90deg);
   }
   .listing-head {