style(css): 移除梦幻效果并优化主题样式

- 删除了全局的梦幻光晕效果和相关动画
- 移除了话题卡片的渐变背景和发光效果
- 简化了列表容器的背景样式和阴影效果
- 调整了话题卡片悬停状态的视觉效果
- 优化了分类标签的颜色配置方式
- 更新了选中状态的边框颜色和透明度设置

scss/main.scss

@@ -2,8 +2,6 @@
 
 :root {
   --main-grid-gap: 0.5em;
-  --dream-glow-a: rgb(var(--tertiary-rgb) / 0.24);
-  --dream-glow-b: rgb(var(--tertiary-rgb) / 0.18);
 }
 
 html:not(:has(.has-full-page-chat)) {
@@ -16,72 +14,12 @@ html:not(:has(.has-full-page-chat)) {
 
 body {
   -webkit-font-smoothing: antialiased;
-  position: relative;
 
   @include viewport.until(sm) {
     background-color: var(--d-content-background);
   }
 }
 
-body:not(.has-full-page-chat, .wizard)::before,
-body:not(.has-full-page-chat, .wizard)::after {
-  content: "";
-  position: fixed;
-  width: min(42vw, 32rem);
-  aspect-ratio: 1 / 1;
-  border-radius: 999px;
-  filter: blur(56px);
-  pointer-events: none;
-  z-index: 0;
-}
-
-body:not(.has-full-page-chat, .wizard)::before {
-  top: 5rem;
-  left: -8rem;
-  background: radial-gradient(circle at 30% 30%, var(--dream-glow-a), transparent 62%);
-  animation: dreamy-float-a 18s ease-in-out infinite alternate;
-}
-
-body:not(.has-full-page-chat, .wizard)::after {
-  right: -6rem;
-  bottom: 2rem;
-  background: radial-gradient(circle at 65% 35%, var(--dream-glow-b), transparent 58%);
-  animation: dreamy-float-b 22s ease-in-out infinite alternate;
-}
-
-.d-header-wrap,
-#main-outlet-wrapper,
-.sidebar-wrapper,
-.sidebar-hamburger-dropdown {
-  position: relative;
-  z-index: 1;
-}
-
-@keyframes dreamy-float-a {
-  from {
-    transform: translate3d(0, 0, 0) scale(1);
-  }
-  to {
-    transform: translate3d(3rem, -1.5rem, 0) scale(1.08);
-  }
-}
-
-@keyframes dreamy-float-b {
-  from {
-    transform: translate3d(0, 0, 0) scale(1);
-  }
-  to {
-    transform: translate3d(-2.5rem, 2rem, 0) scale(1.1);
-  }
-}
-
-@media (prefers-reduced-motion: reduce) {
-  body:not(.has-full-page-chat, .wizard)::before,
-  body:not(.has-full-page-chat, .wizard)::after {
-    animation: none;
-  }
-}
-
 #main-outlet-wrapper {
   gap: var(--main-grid-gap);
 }