feat(sidebar): add group-by-type toggle to installed extensions section

- Add group-by-type button to extensions category header (mirrors the
  agent group-by-kind pattern) — syncs with the extensions page Switch
  via shared SidebarDataContext state
- Relocate both group and refresh controls to sit left-aligned
  immediately after the title for both Agent and Extensions sections
- Add plugins.groupByTypeShort i18n key to all 8 locales

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/i18n/locales/en-US.ts

@@ -540,6 +540,7 @@ const enUS = {
     kindBadgeAgent: 'Agent',
     kindBadgePipeline: 'Pipeline',
     groupByKind: 'Group by type',
+    groupByKindShort: 'Group',
     pipelineTypeDescription:
       'Keep the existing no-code message pipeline for backward compatibility. It only handles message events.',
     allEvents: 'Supports all EBA events',
@@ -602,6 +603,7 @@ const enUS = {
     noExtensionInstalled: 'No extensions installed',
     loadingExtensions: 'Loading extensions...',
     groupByType: 'Group by format',
+    groupByTypeShort: 'Group',
     pluginConfig: 'Plugin Configuration',
     pluginSort: 'Plugin Sort',
     pluginSortDescription: