perf(frontend): add virtual scrolling to DataTable

Replace direct row rendering with @tanstack/vue-virtual. The table
now only renders visible rows (~20) via padding <tr> placeholders,
eliminating the rendering bottleneck when displaying 100+ rows with
heavy cell components.

Key changes:
- DataTable.vue: integrate useVirtualizer (always-on), virtual row
  template with measureElement for variable row heights, defineExpose
  virtualizer/sortedData for external access, overflow-y/flex CSS
- useSwipeSelect.ts: dual-mode support via optional
  SwipeSelectVirtualContext — data-driven row index lookup and
  selection range when virtualizer is present, original DOM-based
  path preserved for callers that don't pass virtualContext

frontend/package.json

@@ -16,6 +16,7 @@
   },
   "dependencies": {
     "@lobehub/icons": "^4.0.2",
+    "@tanstack/vue-virtual": "^3.13.23",
     "@vueuse/core": "^10.7.0",
     "axios": "^1.13.5",
     "chart.js": "^4.4.1",