fix(frontend): Phase 9 — restore index dashboard, fix login/CSRF, port legacy styles

- Index dashboard regains the 8 cards that were lost in the SPA port
  (3X-UI panel info, Operation Hours, System Load, Usage, Overall Speed,
  Total Data, IP Addresses, Connection Stats), plus a Config button that
  shows the live xray config.json. Version display falls back through
  panelUpdateInfo → window.__X_UI_CUR_VER__ → '?' so dev mode isn't blank.
- Xray config no longer hangs on load: useXraySetting surfaces failures
  instead of leaving a perpetual spinner, and the Vite dev proxy stops
  hijacking POST requests to migrated routes (only GETs get bypassed).
- Inbound page no longer throws __asyncLoader/emitsOptions errors —
  inbound.js was missing imports (NumberFormatter, SizeFormatter,
  Wireguard) and InboundList kept emitting after unmount.
- Login round-trip works after logout: a public /csrf-token endpoint
  bootstraps the SPA before authentication, axios caches the token
  module-level, and the dev 401 handler navigates to /login.html
  instead of reloading the dashboard into a redirect loop.
- legacy.css mirrors the legacy panel's surface/text variables so dark
  and ultra-dark themes match main; every SPA entry imports it.

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

frontend/src/pages/index/BackupModal.vue

@@ -67,7 +67,9 @@ function importDb() {
           <template #description>{{ t('pages.index.exportDatabaseDesc') }}</template>
         </a-list-item-meta>
         <a-button type="primary" @click="exportDb">
-          <template #icon><DownloadOutlined /></template>
+          <template #icon>
+            <DownloadOutlined />
+          </template>
         </a-button>
       </a-list-item>
 
@@ -77,7 +79,9 @@ function importDb() {
           <template #description>{{ t('pages.index.importDatabaseDesc') }}</template>
         </a-list-item-meta>
         <a-button type="primary" @click="importDb">
-          <template #icon><UploadOutlined /></template>
+          <template #icon>
+            <UploadOutlined />
+          </template>
         </a-button>
       </a-list-item>
     </a-list>
@@ -85,6 +89,13 @@ function importDb() {
 </template>
 
 <style scoped>
-.backup-list { width: 100%; }
-.backup-item { display: flex; align-items: center; gap: 16px; }
+.backup-list {
+  width: 100%;
+}
+
+.backup-item {
+  display: flex;
+  align-items: center;
+  gap: 16px;
+}
 </style>