feat(ui): content-first shelf redesign — responsive cover grid, hover overlays, format badges, skeletons, sticky blurred top bar, brand login, SVG icon set, animated toasts

frontend/src/index.css

@@ -7,7 +7,17 @@ body,
 }
 body {
   @apply bg-stone-950 text-stone-100 antialiased;
+  /* 顶部一抹极淡的琥珀氛围光,避免大面积纯黑的"朴素感" */
+  background-image: radial-gradient(60rem 28rem at 50% -8rem, rgb(217 119 6 / 0.07), transparent 70%);
+  background-repeat: no-repeat;
 }
+
+/* 入场:卡片/区块轻微上浮淡入(列表 stagger 用 style.animationDelay) */
+@keyframes fx-rise {
+  from { opacity: 0; transform: translateY(8px); }
+  to { opacity: 1; transform: none; }
+}
+.fx-rise { animation: fx-rise 0.35s cubic-bezier(0.22, 1, 0.36, 1) both; }
 ::-webkit-scrollbar {
   width: 10px;
   height: 10px;
@@ -57,6 +67,7 @@ body {
 @media (prefers-reduced-motion: reduce) {
   .rd-sheet { animation: none; }
   .rd-rise-anim { transition: none !important; }
+  .fx-rise { animation: none; }
 }
 
 /* markdown 正文(仅 .md-body 作用域) */