feat: add marquee selection box overlay during drag-to-select

Show a semi-transparent blue rectangle overlay while dragging to
select rows, matching the project's primary color theme with dark
mode support. The box spans the full table width from drag start
to current mouse position.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/views/admin/ProxiesView.vue

@@ -88,6 +88,7 @@
       </template>
 
       <template #table>
+        <div ref="proxyTableRef">
         <DataTable :columns="columns" :data="proxies" :loading="loading">
           <template #header-select>
             <input
@@ -325,6 +326,7 @@
             />
           </template>
         </DataTable>
+        </div>
       </template>
 
       <template #pagination>
@@ -880,6 +882,7 @@ import Select from '@/components/common/Select.vue'
 import Icon from '@/components/icons/Icon.vue'
 import PlatformTypeBadge from '@/components/common/PlatformTypeBadge.vue'
 import { useClipboard } from '@/composables/useClipboard'
+import { useSwipeSelect } from '@/composables/useSwipeSelect'
 
 const { t } = useI18n()
 const appStore = useAppStore()
@@ -959,6 +962,12 @@ const qualityCheckingProxyIds = ref<Set<number>>(new Set())
 const batchTesting = ref(false)
 const batchQualityChecking = ref(false)
 const selectedProxyIds = ref<Set<number>>(new Set())
+const proxyTableRef = ref<HTMLElement | null>(null)
+useSwipeSelect(proxyTableRef, {
+  isSelected: (id) => selectedProxyIds.value.has(id),
+  select: (id) => { const next = new Set(selectedProxyIds.value); next.add(id); selectedProxyIds.value = next },
+  deselect: (id) => { const next = new Set(selectedProxyIds.value); next.delete(id); selectedProxyIds.value = next }
+})
 const accountsProxy = ref<Proxy | null>(null)
 const proxyAccounts = ref<ProxyAccountSummary[]>([])
 const accountsLoading = ref(false)