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.

app/[locale]/settings/page.tsx

@@ -352,7 +352,7 @@ export default function SettingsPage() {
         </div>
 
         {/* Tabs */}
-        <div className="flex-1 overflow-y-auto py-2">
+        <div className="flex-1 overflow-y-auto py-2" data-tour="settings-tabs">
           <div className="px-2 space-y-0.5">
             {groupedTabs.map((group, groupIndex) => (
               <div key={group.group}>