feat(frontend): Phase 5c-iv (a) — panel update / logs / backup modals

Adds three of the six dashboard modals plus a Quick Actions card
that surfaces them. The remaining three (xray logs, version picker,
CPU history sparkline) ship in 5c-iv-b.

- PanelUpdateModal.vue — current vs latest version, "update now"
  button. Confirm dialog → POST /panel/api/server/updatePanel,
  then poll /server/status for up to 90s until the new panel
  answers, then reload.
- LogModal.vue — panel logs viewer. Filters: rows (10-500), level
  (debug/info/notice/warning/error), syslog toggle. Auto-fetches
  on open and on every filter change. Color-coded timestamps and
  levels via inline span styles. Download button writes the raw
  log to x-ui.log via FileManager.downloadTextFile.
- BackupModal.vue — db export (window.location to /getDb) and
  import (FormData upload to /importDB, then panel restart + reload).
- Quick Actions card surfaces Logs / Backup / Update buttons and
  shows an orange update badge (extra slot) when an update is
  available.

Modal-busy pattern: long-running operations (update, import) emit
a `busy` event with a tip; IndexPage flips its a-spin overlay so the
user sees a loading message while the panel is restarting.

AD-Vue 4 changes:
- v-model on <a-modal> renamed to v-model:open
- v-model on <a-input>/<a-select>/<a-checkbox> uses the named
  v-model:value / v-model:checked pattern
- <a-icon type="..."> dropped — explicit Ant icon imports
  (BarsOutlined, CloudServerOutlined, CloudDownloadOutlined,
  DownloadOutlined, UploadOutlined, SyncOutlined)
- Modal.confirm() replaces this.$confirm() since setup() has no `this`

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/pages/index/BackupModal.vue

@@ -0,0 +1,87 @@
+<script setup>
+import { DownloadOutlined, UploadOutlined } from '@ant-design/icons-vue';
+import { HttpUtil, PromiseUtil } from '@/utils';
+
+defineProps({
+  open: { type: Boolean, default: false },
+  basePath: { type: String, default: '' },
+});
+
+const emit = defineEmits(['update:open', 'busy']);
+
+function close() {
+  emit('update:open', false);
+}
+
+function exportDb() {
+  // The Go endpoint streams x-ui.db as a download. Setting
+  // window.location triggers a browser download without leaving
+  // the page (the Go side responds with Content-Disposition: attachment).
+  window.location = '/panel/api/server/getDb';
+}
+
+function importDb() {
+  const fileInput = document.createElement('input');
+  fileInput.type = 'file';
+  fileInput.accept = '.db';
+  fileInput.addEventListener('change', async (e) => {
+    const dbFile = e.target.files?.[0];
+    if (!dbFile) return;
+
+    const formData = new FormData();
+    formData.append('db', dbFile);
+
+    close();
+    emit('busy', { busy: true, tip: 'Importing database…' });
+
+    const upload = await HttpUtil.post('/panel/api/server/importDB', formData, {
+      headers: { 'Content-Type': 'multipart/form-data' },
+    });
+    if (!upload?.success) {
+      emit('busy', { busy: false });
+      return;
+    }
+
+    emit('busy', { busy: true, tip: 'Restarting panel…' });
+    const restart = await HttpUtil.post('/panel/setting/restartPanel');
+    if (restart?.success) {
+      await PromiseUtil.sleep(5000);
+      window.location.reload();
+    } else {
+      emit('busy', { busy: false });
+    }
+  });
+  fileInput.click();
+}
+</script>
+
+<template>
+  <a-modal :open="open" title="Database backup & restore" :closable="true" :footer="null" @cancel="close">
+    <a-list bordered class="backup-list">
+      <a-list-item class="backup-item">
+        <a-list-item-meta>
+          <template #title>Back up</template>
+          <template #description>Click to download a .db file containing a backup of your current database to your device.</template>
+        </a-list-item-meta>
+        <a-button type="primary" @click="exportDb">
+          <template #icon><DownloadOutlined /></template>
+        </a-button>
+      </a-list-item>
+
+      <a-list-item class="backup-item">
+        <a-list-item-meta>
+          <template #title>Restore</template>
+          <template #description>Click to upload a .db file. The panel restarts after restore — your session will reconnect automatically.</template>
+        </a-list-item-meta>
+        <a-button type="primary" @click="importDb">
+          <template #icon><UploadOutlined /></template>
+        </a-button>
+      </a-list-item>
+    </a-list>
+  </a-modal>
+</template>
+
+<style scoped>
+.backup-list { width: 100%; }
+.backup-item { display: flex; align-items: center; gap: 16px; }
+</style>