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.

components/email/email-composer.tsx

@@ -886,6 +886,7 @@ export function EmailComposer({
   return (
     <div
       className={cn("flex flex-col h-full bg-background relative", className)}
+      data-tour="composer"
       onDragEnter={handleDragEnter}
       onDragLeave={handleDragLeave}
       onDragOver={handleDragOver}