style(ui): 数据表格统一细节——表头规格、选中行高亮

- 全站表格表头统一为 11px/700/0.07em 次要色，上下 11px
- 多选表格（用户/违禁词/兑换码）选中行加灰底 + 左缘黑条高亮
- 未显式设色的 td 默认次要文本色

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

frontend/src/views/BannedWordsView.vue

@@ -154,7 +154,7 @@ onMounted(load)
         <tbody>
           <tr v-if="loading && !items.length"><td colspan="5" class="text-center text-xs text-white/40 py-10">加载中…</td></tr>
           <tr v-else-if="!items.length"><td colspan="5" class="text-center text-xs text-white/40 py-10">还没有违禁词</td></tr>
-          <tr v-for="w in pagedItems" :key="w.id" class="border-b border-white/[0.04] hover:bg-white/[0.03] transition-colors">
+          <tr v-for="w in pagedItems" :key="w.id" class="border-b border-white/[0.04] hover:bg-white/[0.03] transition-colors" :class="selected.has(w.id) && 'row-on'">
             <td class="px-3 py-3.5 align-middle text-center">
               <input type="checkbox" :checked="selected.has(w.id)" @change="toggleSelect(w.id)" @click.stop class="chk" />
             </td>