feat: add demo data for emails, files, filters, identities, mailboxes, vacation responses, and JMAP client interface

- Created demo emails with various states (inbox, sent, drafts, trash, etc.) in `emails.ts`.
- Added demo file nodes representing directories and files in `files.ts`.
- Implemented demo Sieve capabilities and scripts in `filters.ts`.
- Defined demo identities for users in `identities.ts`.
- Established demo mailboxes with permissions and counts in `mailboxes.ts`.
- Created a demo vacation response in `vacation.ts`.
- Introduced a comprehensive JMAP client interface in `client-interface.ts` to standardize interactions with the JMAP API.

lib/demo/demo-data.ts

@@ -0,0 +1,45 @@
+import { cloneFixtures } from './demo-utils';
+import { createDemoMailboxes } from './fixtures/mailboxes';
+import { createDemoEmails } from './fixtures/emails';
+import { createDemoContacts, createDemoAddressBooks } from './fixtures/contacts';
+import { createDemoCalendars, createDemoCalendarEvents } from './fixtures/calendars';
+import { createDemoIdentities } from './fixtures/identities';
+import { createDemoSieveScripts, createDemoSieveCapabilities, createDemoSieveContent } from './fixtures/filters';
+import { createDemoFileNodes } from './fixtures/files';
+import { createDemoVacationResponse } from './fixtures/vacation';
+
+import type { Email, Mailbox, ContactCard, AddressBook, Calendar, CalendarEvent, Identity, VacationResponse, FileNode } from '@/lib/jmap/types';
+import type { SieveScript, SieveCapabilities } from '@/lib/jmap/sieve-types';
+
+export interface DemoData {
+  mailboxes: Mailbox[];
+  emails: Email[];
+  contacts: ContactCard[];
+  addressBooks: AddressBook[];
+  calendars: Calendar[];
+  calendarEvents: CalendarEvent[];
+  identities: Identity[];
+  sieveScripts: SieveScript[];
+  sieveCapabilities: SieveCapabilities;
+  sieveContent: Record<string, string>;
+  fileNodes: FileNode[];
+  vacationResponse: VacationResponse;
+}
+
+/** Return a fresh deep-cloned copy of all demo data. */
+export function getDemoData(): DemoData {
+  return cloneFixtures({
+    mailboxes: createDemoMailboxes(),
+    emails: createDemoEmails(),
+    contacts: createDemoContacts(),
+    addressBooks: createDemoAddressBooks(),
+    calendars: createDemoCalendars(),
+    calendarEvents: createDemoCalendarEvents(),
+    identities: createDemoIdentities(),
+    sieveScripts: createDemoSieveScripts(),
+    sieveCapabilities: createDemoSieveCapabilities(),
+    sieveContent: createDemoSieveContent(),
+    fileNodes: createDemoFileNodes(),
+    vacationResponse: createDemoVacationResponse(),
+  });
+}