style: 全局 UI 主题皮肤重构与样式模块化

引入 Element Plus 主题定制和主题皮肤 composable，将全局
样式拆分为组件级独立 CSS 文件（侧边栏、顶栏、工作台等），
统一色彩变量和间距规范，重构所有视图和组件样式以适配新
主题系统，优化图表和知识图谱组件视觉表现，提取审计和差
旅报销相关子组件。

web/src/assets/styles/element-plus-theme.css

@@ -0,0 +1,131 @@
+:root {
+  --theme-primary: #3a7ca5;
+  --theme-primary-hover: #2f6d95;
+  --theme-primary-active: #255b7d;
+  --theme-primary-soft: #eaf4fa;
+  --theme-primary-soft-strong: #d4e8f3;
+  --theme-primary-rgb: 58, 124, 165;
+  --theme-focus-ring: rgba(58, 124, 165, 0.12);
+  --el-color-primary: var(--theme-primary);
+  --el-color-primary-light-3: var(--theme-primary-hover);
+  --el-color-primary-light-5: var(--theme-primary-light-5);
+  --el-color-primary-light-7: var(--theme-primary-soft-strong);
+  --el-color-primary-light-8: var(--theme-primary-soft);
+  --el-color-primary-light-9: var(--theme-primary-light-9);
+  --el-color-primary-dark-2: var(--theme-primary-active);
+  --el-color-success: var(--success);
+  --el-color-success-light-9: var(--success-soft);
+  --el-color-warning: var(--warning);
+  --el-color-warning-light-9: var(--warning-soft);
+  --el-color-danger: var(--danger);
+  --el-color-danger-light-9: var(--danger-soft);
+  --el-color-info: var(--info);
+  --el-border-radius-base: 4px;
+  --el-border-radius-small: 3px;
+  --el-border-radius-round: 4px;
+  --el-border-color: var(--line-strong);
+  --el-border-color-light: var(--line);
+  --el-border-color-lighter: #edf2f7;
+  --el-fill-color-light: var(--bg);
+  --el-fill-color-lighter: var(--surface-soft);
+  --el-fill-color-blank: var(--surface);
+  --el-text-color-primary: var(--ink);
+  --el-text-color-regular: var(--text);
+  --el-text-color-secondary: var(--muted);
+  --el-font-family: Inter, "SF Pro Text", "Segoe UI", "Microsoft YaHei", "PingFang SC", sans-serif;
+  --el-font-size-base: 14px;
+  --el-box-shadow-light: 0 8px 22px rgba(15, 23, 42, 0.08);
+  --el-box-shadow-lighter: 0 4px 14px rgba(15, 23, 42, 0.06);
+  --el-transition-duration: 180ms;
+  --el-transition-function-ease-in-out-bezier: cubic-bezier(0.2, 0, 0, 1);
+}
+
+.el-button {
+  font-weight: 600;
+  letter-spacing: 0;
+}
+
+.el-button,
+.el-input__wrapper,
+.el-select__wrapper,
+.el-textarea__inner,
+.el-date-editor.el-input__wrapper,
+.el-popover.el-popper,
+.el-popper.is-light,
+.el-message-box,
+.el-dialog {
+  border-radius: 4px;
+}
+
+.el-input__wrapper,
+.el-select__wrapper {
+  min-height: 34px;
+  box-shadow: 0 0 0 1px var(--el-border-color) inset;
+  transition:
+    box-shadow 160ms var(--ease),
+    background-color 160ms var(--ease),
+    border-color 160ms var(--ease);
+}
+
+.el-input__wrapper:hover,
+.el-select__wrapper:hover {
+  box-shadow: 0 0 0 1px #b8c2d2 inset;
+}
+
+.el-input__wrapper.is-focus,
+.el-select__wrapper.is-focused {
+  box-shadow:
+    0 0 0 1px var(--el-color-primary) inset,
+    0 0 0 3px var(--theme-focus-ring);
+}
+
+.el-select-dropdown,
+.el-picker__popper,
+.el-dropdown__popper,
+.el-popover.el-popper {
+  border: 1px solid rgba(148, 163, 184, 0.26);
+  box-shadow: 0 16px 36px rgba(15, 23, 42, 0.12);
+}
+
+.el-select-dropdown__item {
+  height: 34px;
+  color: #334155;
+  font-size: 13px;
+  line-height: 34px;
+}
+
+.el-select-dropdown__item.is-hovering {
+  background: #f1f5f9;
+}
+
+.el-select-dropdown__item.is-selected {
+  background: var(--theme-primary-soft);
+  color: var(--theme-primary-active);
+  font-weight: 700;
+}
+
+.el-scrollbar__bar {
+  opacity: 0.28;
+}
+
+.el-overlay {
+  background-color: rgba(15, 23, 42, 0.42);
+}
+
+.el-dialog,
+.el-message-box {
+  box-shadow: 0 24px 70px rgba(15, 23, 42, 0.18);
+}
+
+.el-table {
+  --el-table-header-bg-color: #f8fafc;
+  --el-table-header-text-color: #334155;
+  --el-table-row-hover-bg-color: #f8fafc;
+  color: #334155;
+}
+
+.el-pagination {
+  --el-pagination-button-bg-color: #ffffff;
+  --el-pagination-hover-color: var(--theme-primary-active);
+  font-weight: 600;
+}