feat(sidebar): add group-by-kind toggle to Agent section

Add a toggle (left of the "+" button) that groups the Agent section by
kind, showing "Agent" and "Pipeline" sub-headers. State persists in
localStorage, mirroring the extensions group-by-type pattern.

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

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

@@ -519,6 +519,7 @@ const enUS = {
     pipelineType: 'Pipeline',
     kindBadgeAgent: 'Agent',
     kindBadgePipeline: 'Pipeline',
+    groupByKind: 'Group by type',
     pipelineTypeDescription:
       'Keep the existing no-code message pipeline for backward compatibility. It only handles message events.',
     allEvents: 'Supports all EBA events',

web/src/i18n/locales/ja-JP.ts

@@ -503,6 +503,7 @@ const jaJP = {
     pipelineType: 'Pipeline',
     kindBadgeAgent: 'Agent',
     kindBadgePipeline: 'パイプライン',
+    groupByKind: 'タイプ別にグループ化',
     pipelineTypeDescription:
       '既存のノーコードメッセージ Pipeline を互換性のため保持します。メッセージイベントのみ処理できます。',
     allEvents: 'すべての EBA イベントに対応',

web/src/i18n/locales/zh-Hans.ts

@@ -499,6 +499,7 @@ const zhHans = {
     pipelineType: 'Pipeline',
     kindBadgeAgent: 'Agent',
     kindBadgePipeline: '流水线',
+    groupByKind: '按类型分组',
     pipelineTypeDescription:
       '保留现有无代码消息流水线，兼容旧配置，只能处理消息事件。',
     allEvents: '支持全部 EBA 事件',