fix(sidebar): show loading state during batch export

Export button shows 'Exporting N sessions…' text and becomes disabled
while fetching blobs and building the zip. An info toast also fires
immediately so the user knows work is in progress.

desktop/src/components/layout/Sidebar.tsx

@@ -103,6 +103,7 @@ export function Sidebar({ isMobile = false, onRequestClose }: SidebarProps) {
   const [pendingDeleteSessionId, setPendingDeleteSessionId] = useState<string | null>(null)
   const [pendingBatchDeleteSessionIds, setPendingBatchDeleteSessionIds] = useState<string[] | null>(null)
   const [isBatchDeleting, setIsBatchDeleting] = useState(false)
+  const [isBatchExporting, setIsBatchExporting] = useState(false)
   const [pendingClearProjectKey, setPendingClearProjectKey] = useState<string | null>(null)
   const [isClearingProject, setIsClearingProject] = useState(false)
   const [renamingId, setRenamingId] = useState<string | null>(null)
@@ -642,6 +643,8 @@ export function Sidebar({ isMobile = false, onRequestClose }: SidebarProps) {
     }
 
     // Multiple sessions: collect blobs, pack into zip
+    setIsBatchExporting(true)
+    addToast({ type: 'info', message: t('sidebar.batchExporting', { count: ids.length }) })
     try {
       const { zipSync } = await import('fflate')
       const entries: Record<string, Uint8Array> = {}
@@ -687,6 +690,8 @@ export function Sidebar({ isMobile = false, onRequestClose }: SidebarProps) {
           error: error instanceof Error ? error.message : String(error),
         }),
       })
+    } finally {
+      setIsBatchExporting(false)
     }
   }, [addToast, handleExitBatchMode, handleExportSession, selectedSessionIds, sessions, t])
 
@@ -999,10 +1004,10 @@ export function Sidebar({ isMobile = false, onRequestClose }: SidebarProps) {
                   <button
                     type="button"
                     onClick={() => void handleBatchExport()}
-                    disabled={selectedCount === 0}
+                    disabled={selectedCount === 0 || isBatchExporting}
                     className="rounded-md border border-[var(--color-border)] px-2 py-1.5 text-xs font-medium text-[var(--color-text-secondary)] transition-colors hover:bg-[var(--color-surface-hover)] disabled:opacity-50"
                   >
-                    {t('sidebar.batchExportSelected', { count: selectedCount })}
+                    {isBatchExporting ? t('sidebar.batchExporting', { count: selectedCount }) : t('sidebar.batchExportSelected', { count: selectedCount })}
                   </button>
                   <button
                     type="button"

desktop/src/i18n/locales/en.ts

@@ -93,6 +93,7 @@ export const en = {
   'sidebar.batchSelectGroup': 'Select {group}',
   'sidebar.batchDeleteSelected': 'Delete selected ({count})',
   'sidebar.batchExportSelected': 'Export selected ({count})',
+  'sidebar.batchExporting': 'Exporting {count} sessions…',
   'sidebar.exportProjectSessions': 'Export sessions…',
   'sidebar.batchDeleteConfirm': 'Delete {count} sessions? This cannot be undone.',
   'sidebar.batchDeleteConfirmBody': 'The following sessions will be deleted:',

desktop/src/i18n/locales/jp.ts

@@ -95,6 +95,7 @@ export const jp: Record<TranslationKey, string> = {
   'sidebar.batchSelectGroup': '{group} を選択',
   'sidebar.batchDeleteSelected': '選択項目を削除 ({count})',
   'sidebar.batchExportSelected': '選択項目をエクスポート ({count})',
+  'sidebar.batchExporting': '{count} 件のセッションをエクスポート中…',
   'sidebar.exportProjectSessions': 'セッションをエクスポート…',
   'sidebar.batchDeleteConfirm': '{count} 件のセッションを削除しますか？この操作は取り消せません。',
   'sidebar.batchDeleteConfirmBody': '以下のセッションが削除されます:',

desktop/src/i18n/locales/kr.ts

@@ -95,6 +95,7 @@ export const kr: Record<TranslationKey, string> = {
   'sidebar.batchSelectGroup': '{group} 선택',
   'sidebar.batchDeleteSelected': '선택 항목 삭제 ({count})',
   'sidebar.batchExportSelected': '선택 항목 내보내기 ({count})',
+  'sidebar.batchExporting': '{count}개 세션 내보내는 중…',
   'sidebar.exportProjectSessions': '세션 내보내기…',
   'sidebar.batchDeleteConfirm': '{count}개의 세션을 삭제하시겠습니까? 이 작업은 취소할 수 없습니다.',
   'sidebar.batchDeleteConfirmBody': '다음 세션이 삭제됩니다:',

desktop/src/i18n/locales/zh-TW.ts

@@ -95,6 +95,7 @@ export const zh: Record<TranslationKey, string> = {
   'sidebar.batchSelectGroup': '選擇{group}',
   'sidebar.batchDeleteSelected': '刪除已選 ({count})',
   'sidebar.batchExportSelected': '匯出已選 ({count})',
+  'sidebar.batchExporting': '正在匯出 {count} 個會話…',
   'sidebar.exportProjectSessions': '匯出會話…',
   'sidebar.batchDeleteConfirm': '確定要刪除 {count} 個會話嗎？此操作不可撤銷。',
   'sidebar.batchDeleteConfirmBody': '以下會話將被刪除：',

desktop/src/i18n/locales/zh.ts

@@ -95,6 +95,7 @@ export const zh: Record<TranslationKey, string> = {
   'sidebar.batchSelectGroup': '选择{group}',
   'sidebar.batchDeleteSelected': '删除已选 ({count})',
   'sidebar.batchExportSelected': '导出已选 ({count})',
+  'sidebar.batchExporting': '正在导出 {count} 个会话…',
   'sidebar.exportProjectSessions': '导出会话…',
   'sidebar.batchDeleteConfirm': '确定要删除 {count} 个会话吗？此操作不可撤销。',
   'sidebar.batchDeleteConfirmBody': '以下会话将被删除：',