后台管理重塑 + 主题 / 皮肤双轴 + a11y 与编辑器增强

Backend
- Post 加 cover_url，Tag 加 color；老库 ALTER 兼容
- admin API: GET /api/admin/dashboard，POST /bulk，POST /tags/:id/merge，
  PUT /tags/:id 接 {name,color}，Settings 加 light_skin_id（兼容老 theme_id）
- 白名单兜底（非法 light_skin_id 落 paper）
- 新增合并 / Dashboard / Theme 测试覆盖

Frontend
- AdminLayout 改为侧边栏布局；新增 Dashboard 总览页
- PostsView 卡片化预览 + 筛选 chip + 批量操作 + 排序
- EditorView 增强：封面图 / WYSIWYG↔MD 双模式 / 实时大纲 / 字数统计 /
  自动保存条 / ⌘S / unsaved 守卫（beforeunload + beforeRouteLeave）
- TagsView 加色板 + 合并到目标
- SettingsView 主题外观改为「亮色皮肤」三选一 + 「暗色皮肤」固定墨色说明
- 新增 CommandPalette（⌘K）+ ShortcutsPanel（?）
- api.js 接新接口；router.js 拆 /admin → /admin/posts

主题 / 皮肤双轴
- site.js: themeMode（light/dark/auto）+ light_skin_id；data-theme 前台，
  data-admin-theme 后台（仅跟随 mode 切明暗）
- styles.css: :root[data-theme] 四套皮肤 + :root[data-admin-theme=dark] 后台墨感
- 修 sticky head / ThemeSwitcher / 表单 / 批量条 等 token 引用
- 后台用独立 --admin-* 系列，与前台主题解耦
- 左栏底部放 inline 形态 ThemeSwitcher（图标按钮 36×36），mobile 保留浮窗

a11y
- 全局 :focus-visible 描边（前后台跟随 token）
- prefers-reduced-motion 全局降级
- color-scheme 随主题切
- meta theme-color 双套（light/dark）
- 命令面板 / 快捷键面板：role=dialog aria-modal aria-label + 搜索框 aria-label
- icon-only 按钮加 aria-label（tag × / 清除选择 / 移除封面等）
- 输入框 aria-label + spellcheck=false
- PostsView 筛选同步 URL（可分享、可刷新保留）
- img width/height + loading=lazy
- utils.js 用 Intl.DateTimeFormat（zh-CN / sv-SE）

frontend/src/admin/CommandPalette.vue

@@ -0,0 +1,133 @@
+<script setup>
+import { computed, nextTick, onMounted, onBeforeUnmount, ref } from 'vue'
+import { useRouter } from 'vue-router'
+import { adminApi } from '../api'
+
+const emit = defineEmits(['close'])
+const router = useRouter()
+
+const query = ref('')
+const inputEl = ref(null)
+const idx = ref(0)
+const recentDrafts = ref([])
+
+const baseCommands = [
+  { id: 'go-new', label: '写新文章', hint: 'N', action: () => router.push('/admin/new') },
+  { id: 'go-dashboard', label: '总览', hint: 'G D', action: () => router.push('/admin') },
+  { id: 'go-posts', label: '文章列表', hint: 'G P', action: () => router.push('/admin/posts') },
+  { id: 'go-tags', label: '标签管理', hint: 'G T', action: () => router.push('/admin/tags') },
+  { id: 'go-settings', label: '设置', hint: 'G S', action: () => router.push('/admin/settings') },
+  { id: 'go-site', label: '前台', hint: 'G W', action: () => (window.location.href = '/') }
+]
+
+async function loadContext() {
+  try {
+    const d = await adminApi.dashboard()
+    recentDrafts.value = (d.recent_drafts || []).map((p) => ({
+      id: 'edit-' + p.id,
+      label: p.title || '(无题草稿)',
+      hint: p.kind === 'short' ? '短文' : '长文',
+      action: () => router.push('/admin/' + p.id)
+    }))
+  } catch (e) {
+    /* ignore */
+  }
+}
+
+// Flatten items into [{sec, item, idx}] so we can render sections but still
+// track a single cursor across the whole list.
+const flat = computed(() => {
+  const q = query.value.trim().toLowerCase()
+  const sections = [
+    { name: '命令', items: baseCommands },
+    { name: '最近草稿', items: recentDrafts.value }
+  ]
+  const out = []
+  for (const sec of sections) {
+    for (const it of sec.items) {
+      if (q && !it.label.toLowerCase().includes(q)) continue
+      out.push({ section: sec.name, item: it })
+    }
+  }
+  return out
+})
+
+// Re-group for display, while preserving the flat indices.
+const sections = computed(() => {
+  const out = []
+  let i = 0
+  let lastName = null
+  for (const e of flat.value) {
+    if (e.section !== lastName) {
+      out.push({ name: e.section, entries: [] })
+      lastName = e.section
+    }
+    out[out.length - 1].entries.push({ ...e.item, _idx: i })
+    i++
+  }
+  return out
+})
+
+function run(item) {
+  item.action()
+  emit('close')
+}
+
+function onKey(e) {
+  if (e.key === 'Escape') {
+    e.preventDefault()
+    emit('close')
+  } else if (e.key === 'ArrowDown') {
+    e.preventDefault()
+    idx.value = Math.min(flat.value.length - 1, idx.value + 1)
+  } else if (e.key === 'ArrowUp') {
+    e.preventDefault()
+    idx.value = Math.max(0, idx.value - 1)
+  } else if (e.key === 'Enter') {
+    e.preventDefault()
+    const it = flat.value[idx.value]
+    if (it) run(it.item)
+  }
+}
+
+onMounted(async () => {
+  await loadContext()
+  await nextTick()
+  inputEl.value?.focus()
+  window.addEventListener('keydown', onKey)
+})
+onBeforeUnmount(() => window.removeEventListener('keydown', onKey))
+</script>
+
+<template>
+  <div class="cmd-overlay" role="dialog" aria-modal="true" aria-label="命令面板" @click.self="emit('close')">
+    <div class="cmd-panel">
+      <input
+        ref="inputEl"
+        v-model="query"
+        placeholder="输入命令、文章标题…"
+        aria-label="搜索命令和文章"
+        @input="idx = 0"
+      />
+      <div class="cmd-list">
+        <template v-for="(sec, si) in sections" :key="si">
+          <div style="padding: 8px 18px 4px; font-size: 11px; color: var(--admin-muted); letter-spacing: 0.08em; text-transform: uppercase;">
+            {{ sec.name }}
+          </div>
+          <div
+            v-for="(it, ii) in sec.entries"
+            :key="it.id"
+            class="row"
+            :class="{ on: idx === it._idx }"
+            @click="run(it)"
+            @mouseenter="idx = it._idx"
+          >
+            <span class="label">{{ it.label }}</span>
+            <span class="hint">{{ it.hint }}</span>
+          </div>
+        </template>
+        <div v-if="!flat.length" class="empty">没找到匹配的命令</div>
+      </div>
+    </div>
+  </div>
+</template>