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

lib/jmap/client.ts

@@ -1,4 +1,4 @@
-import type { Email, Mailbox, StateChange, AccountStates, Thread, Identity, EmailAddress, ContactCard, AddressBook, AddressBookRights, VacationResponse, Calendar, CalendarRights, CalendarEvent, CalendarEventFilter, CalendarTask, FileNode, FileNodeFilter, FileNodeRights, Principal, PushSubscription, EmailSubmission, ScheduledEmail, SendEmailResult, SharedAccount } from "./types";
+import type { Email, Mailbox, MailboxRights, StateChange, AccountStates, Thread, Identity, EmailAddress, ContactCard, AddressBook, AddressBookRights, VacationResponse, Calendar, CalendarRights, CalendarEvent, CalendarEventFilter, CalendarTask, FileNode, FileNodeFilter, FileNodeRights, Principal, PushSubscription, EmailSubmission, ScheduledEmail, SendEmailResult, SharedAccount } from "./types";
 import type { SieveScript, SieveCapabilities } from "./sieve-types";
 import type { IJMAPClient } from "./client-interface";
 import { toWildcardQuery } from "./search-utils";
@@ -4426,6 +4426,34 @@ export class JMAPClient implements IJMAPClient {
     }
   }
 
+  /**
+   * Add, update, or remove a principal's rights on a mailbox folder.
+   * Pass `rights: null` to revoke access.
+   */
+  async setMailboxShare(
+    mailboxId: string,
+    principalId: string,
+    rights: MailboxRights | null,
+    targetAccountId?: string,
+  ): Promise<void> {
+    const accountId = targetAccountId || this.accountId;
+    const response = await this.request([
+      ["Mailbox/set", {
+        accountId,
+        update: { [mailboxId]: { [`shareWith/${principalId}`]: rights } },
+      }, "0"],
+    ]);
+
+    const result = response.methodResponses?.[0]?.[1];
+    if (result?.notUpdated?.[mailboxId]) {
+      const err = result.notUpdated[mailboxId];
+      throw new Error(err.description || "Failed to update mailbox share");
+    }
+    if (!result?.updated || !(mailboxId in result.updated)) {
+      throw new Error("Server did not confirm the share update");
+    }
+  }
+
   private async fetchPaginatedContacts(
     accountId: string,
     filter?: Record<string, unknown>,