feat(home): hero carousel with auto-advance, arrows, and dot indicators

Cycles through all in-progress books every 6s; prev/next arrow buttons
overlay the card edges; active dot stretches to a pill; cover fades in
on slide change via {#key} + animate-fade-in; shelf excludes the current
hero to avoid duplication.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ui/src/app.css

@@ -189,6 +189,15 @@ html {
 	display: none;               /* Chrome / Safari / WebKit */
 }
 
+/* ── Hero carousel fade ─────────────────────────────────────────────── */
+@keyframes fade-in {
+	from { opacity: 0; }
+	to   { opacity: 1; }
+}
+.animate-fade-in {
+	animation: fade-in 0.4s ease-out forwards;
+}
+
 /* ── Navigation progress bar ───────────────────────────────────────── */
 @keyframes progress-bar {
 	0%   { width: 0%; opacity: 1; }