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.

stores/vacation-store.ts

@@ -1,5 +1,5 @@
 import { create } from 'zustand';
-import type { JMAPClient } from '@/lib/jmap/client';
+import type { IJMAPClient } from '@/lib/jmap/client-interface';
 
 interface VacationStore {
   isEnabled: boolean;
@@ -13,8 +13,8 @@ interface VacationStore {
   error: string | null;
   isSupported: boolean;
 
-  fetchVacationResponse: (client: JMAPClient) => Promise<void>;
-  updateVacationResponse: (client: JMAPClient, updates: {
+  fetchVacationResponse: (client: IJMAPClient) => Promise<void>;
+  updateVacationResponse: (client: IJMAPClient, updates: {
     isEnabled?: boolean;
     fromDate?: string | null;
     toDate?: string | null;