redesign: site-wide UI/UX overhaul per web-interface-guidelines

- unified design system: focus-visible rings, reduced-motion, color-scheme,
  theme persistence, tightened emerald radius tokens (checkbox circle bug)
- redesigned all pages: Home/Login/Signup/404, dashboard shell, Overview hero
  (time-based gradient), list pages with empty states, form modals, detail pages
- role-scoped navigation: console menu vs admin console with cross-switch
  entries, Chinese route titles and breadcrumbs
- theme switcher (light/dark/auto) via composables/theme, home + dashboard
- state-driven dropdowns (touch-safe logout), menu divider pointer-events fix
- btn-primary unified to black-on-white / white-on-black per theme
- update REFACTOR_PLAN.md (increments 2-6)

frontend/src/styles/main.css

@@ -4,7 +4,87 @@
   themes: light --default, dark, cupcake, emerald, pastel;
 }
 
+/* 收紧 emerald 主题的圆角令牌：默认 selector 圆角过大，小尺寸复选框会渲染成正圆 */
+@plugin "daisyui/theme" {
+  name: "emerald";
+  --radius-selector: 0.5rem;
+  --radius-field: 0.5rem;
+  --radius-box: 0.75rem;
+}
+
+@theme {
+  --font-sans: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto,
+    "Helvetica Neue", Arial, "PingFang SC", "Hiragino Sans GB",
+    "Microsoft YaHei", sans-serif;
+}
+
+/* 深浅色跟随 data-theme，修复滚动条与原生控件配色 */
+html {
+  color-scheme: light;
+}
+
+html[data-theme="dark"] {
+  color-scheme: dark;
+}
+
 body {
   margin: 0;
   padding: 0;
+  background-color: var(--color-base-200);
+  color: var(--color-base-content);
+  -webkit-font-smoothing: antialiased;
+}
+
+/* 移动端去除双击缩放延迟与点击高亮 */
+button,
+a,
+[role="button"],
+input[type="checkbox"],
+input[type="radio"],
+summary {
+  touch-action: manipulation;
+  -webkit-tap-highlight-color: transparent;
+}
+
+/* 统一可见键盘焦点（:focus-visible 不干扰鼠标点击） */
+:where(a, button, input, select, textarea, summary, [tabindex]):focus-visible {
+  outline: 2px solid var(--color-primary);
+  outline-offset: 2px;
+}
+
+/* 弹层内禁止滚动穿透 */
+.modal-box {
+  overscroll-behavior: contain;
+}
+
+/* 普通主按钮统一黑白：浅色主题黑底白字，深色主题白底黑字（特殊按钮 success/error/warning/outline 不受影响） */
+.btn-primary {
+  --btn-color: #171717;
+  --btn-fg: #ffffff;
+  --btn-soft-bg: initial;
+}
+
+.btn-primary:hover {
+  --btn-bg: #000000;
+}
+
+html[data-theme="dark"] .btn-primary {
+  --btn-color: #ffffff;
+  --btn-fg: #171717;
+}
+
+html[data-theme="dark"] .btn-primary:hover {
+  --btn-bg: #e4e4e4;
+}
+
+/* 尊重系统“减弱动态效果”偏好 */
+@media (prefers-reduced-motion: reduce) {
+  *,
+  *::before,
+  *::after {
+    animation-duration: 0.01ms !important;
+    animation-iteration-count: 1 !important;
+    transition-duration: 0.01ms !important;
+    scroll-behavior: auto !important;
+  }
 }