feat(admin): Add group filtering for account listings

- Add groupID parameter to ListAccounts and ListWithFilters methods
- Implement account filtering by group ID in repository query
- Add group query parameter parsing in account handler
- Update all ListAccounts/ListWithFilters call sites with groupID parameter
- Add group filter UI component to AccountTableFilters
- Add i18n translations for group filter label in English and Chinese
- Update API contract and test stubs to reflect new signature
- Enable filtering accounts by their assigned groups in admin panel

frontend/src/i18n/locales/en.ts

@@ -1335,6 +1335,7 @@ export default {
       allPlatforms: 'All Platforms',
       allTypes: 'All Types',
       allStatus: 'All Status',
+      allGroups: 'All Groups',
       oauthType: 'OAuth',
       setupToken: 'Setup Token',
       apiKey: 'API Key',
@@ -1344,7 +1345,7 @@ export default {
       schedulableEnabled: 'Scheduling enabled',
       schedulableDisabled: 'Scheduling disabled',
       failedToToggleSchedulable: 'Failed to toggle scheduling status',
-      allGroups: '{count} groups total',
+      groupCountTotal: '{count} groups total',
       platforms: {
         anthropic: 'Anthropic',
         claude: 'Claude',

frontend/src/i18n/locales/zh.ts

@@ -1426,6 +1426,7 @@ export default {
       allPlatforms: '全部平台',
       allTypes: '全部类型',
       allStatus: '全部状态',
+      allGroups: '全部分组',
       oauthType: 'OAuth',
       // Schedulable toggle
       schedulable: '参与调度',
@@ -1433,7 +1434,7 @@ export default {
       schedulableEnabled: '调度已开启',
       schedulableDisabled: '调度已关闭',
       failedToToggleSchedulable: '切换调度状态失败',
-      allGroups: '共 {count} 个分组',
+      groupCountTotal: '共 {count} 个分组',
       columns: {
         name: '名称',
         platformType: '平台/类型',