feat(frontend): swap QRious for ant-design-vue's a-qrcode

- Migrate SubPage, QrPanel and TwoFactorModal from a QRious canvas to
  <a-qrcode type="svg">, which renders the QR matrix as crispEdges
  SVG rectangles — pixel-perfect at any display size or DPR, no more
  white scan-line artifacts from non-integer canvas scaling
- Drop the now-unused qrious dependency and its manualChunks entry
- Default the panel to ultra-dark on first load (existing user
  preferences in localStorage are preserved)
- Let the sub controller read subpage.html from web/dist/ first and
  fall back to the embedded copy, so Vite rebuilds in dev no longer
  require a Go recompile to refresh the asset hashes

frontend/vite.config.js

@@ -163,7 +163,6 @@ export default defineConfig({
             || id.includes('/node_modules/@vue/')
           ) return 'vendor-vue';
           if (id.includes('dayjs')) return 'vendor-dayjs';
-          if (id.includes('qrious')) return 'vendor-qrious';
           if (id.includes('axios')) return 'vendor-axios';
           if (
             id.includes('vue3-persian-datetime-picker')