feat: P2.3 Folder Sharing + P2.5 Email Import + P2.6 Contact Import + P2.7 Free/Busy

- P2.3: Folder sharing system — ShareFolderDialog, sharing-store, sharing-settings
- P2.5: Email import (.eml, .tgz, .zip) with dedup and progress
- P2.6: Contact import (vCard + CSV) with auto-mapping
- P2.7: Free/Busy view grid with color-coded slots

components/layout/sidebar.tsx

@@ -90,6 +90,7 @@ interface SidebarProps {
   onDeleteFolder?: (mailboxId: string) => void;
   onImportEmail?: (mailboxId: string) => void;
   onRefreshMailboxes?: () => void;
+  onShareFolder?: (mailboxId: string) => void;
   scheduledTotal?: number;
   showScheduledMailbox?: boolean;
   /** True when the unified view spans multiple login accounts (cross-account).
@@ -779,6 +780,7 @@ export function Sidebar({
   onDeleteFolder,
   onImportEmail,
   onRefreshMailboxes,
+  onShareFolder,
   scheduledTotal = 0,
   showScheduledMailbox = false,
   crossAccountActive = false,
@@ -1452,6 +1454,7 @@ export function Sidebar({
         onRenameFolder={onRenameFolder}
         onDeleteFolder={onDeleteFolder}
         onImportEmail={onImportEmail}
+        onShareFolder={onShareFolder}
         onRefresh={onRefreshMailboxes}
       />
     </div>