feat: revamp analytics dashboards and harden database migrations

Add dashboard and overview analytics, health monitoring, provider expense tracking, and announcement updates across the gateway and frontend.

Keep schema migrations free of historical backfills while preserving automatic backfill execution. Bound migration deadlines, run schema preparation before Compose replacement, and anonymize deleted dashboard users.

Include the current documentation cleanup and regression coverage.

frontend/src/features/overview/components/OverviewPagination.vue

@@ -0,0 +1,53 @@
+<template>
+  <div class="flex flex-wrap items-center justify-between gap-3 border-t pt-3 text-xs text-muted-foreground">
+    <span>{{ count(total) }} {{ t('条', 'results') }} · {{ total ? count(offset + 1) : 0 }}-{{ count(Math.min(offset + limit, total)) }}</span>
+    <div class="flex items-center gap-2">
+      <select
+        class="h-8 rounded-md border bg-background px-2"
+        :aria-label="t('每页条数', 'Page size')"
+        :value="limit"
+        @change="$emit('size', Number(($event.target as HTMLSelectElement).value))"
+      >
+        <option
+          v-for="size in [25, 50, 100]"
+          :key="size"
+          :value="size"
+        >
+          {{ size }}
+        </option>
+      </select>
+      <Button
+        size="icon"
+        variant="outline"
+        class="h-8 w-8"
+        :disabled="loading || offset <= 0"
+        :title="t('上一页', 'Previous page')"
+        :aria-label="t('上一页', 'Previous page')"
+        @click="$emit('page', Math.max(0, offset - limit))"
+      >
+        <ChevronLeft class="h-4 w-4" />
+      </Button>
+      <Button
+        size="icon"
+        variant="outline"
+        class="h-8 w-8"
+        :disabled="loading || offset + limit >= total"
+        :title="t('下一页', 'Next page')"
+        :aria-label="t('下一页', 'Next page')"
+        @click="$emit('page', offset + limit)"
+      >
+        <ChevronRight class="h-4 w-4" />
+      </Button>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { ChevronLeft, ChevronRight } from 'lucide-vue-next'
+import { Button } from '@/components/ui'
+import { count } from '../format'
+import { useOverviewI18n } from '../i18n'
+defineProps<{ total: number; offset: number; limit: number; loading?: boolean }>()
+defineEmits<{ page: [offset: number]; size: [limit: number] }>()
+const { t } = useOverviewI18n()
+</script>