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/CpuHistoryModal.vue

@@ -63,21 +63,9 @@ watch(bucket, () => { if (props.open) fetchBucket(); });
     </template>
 
     <div class="cpu-chart-wrap">
-      <Sparkline
-        :data="points"
-        :labels="labels"
-        :vb-width="840"
-        :height="220"
-        :stroke="status?.cpu?.color || '#008771'"
-        :stroke-width="2.2"
-        :show-grid="true"
-        :show-axes="true"
-        :tick-count-x="5"
-        :max-points="points.length || 1"
-        :fill-opacity="0.18"
-        :marker-radius="3.2"
-        :show-tooltip="true"
-      />
+      <Sparkline :data="points" :labels="labels" :vb-width="840" :height="220" :stroke="status?.cpu?.color || '#008771'"
+        :stroke-width="2.2" :show-grid="true" :show-axes="true" :tick-count-x="5" :max-points="points.length || 1"
+        :fill-opacity="0.18" :marker-radius="3.2" :show-tooltip="true" />
       <div class="cpu-chart-meta">
         Timeframe: {{ bucket }} sec per point (total {{ points.length }} points)
       </div>