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-list.tsx

@@ -358,7 +358,7 @@ export function EmailList({
       )}
 
       {/* Email List */}
-      <div ref={parentRef} className="flex-1 overflow-y-auto bg-background relative">
+      <div ref={parentRef} className="flex-1 overflow-y-auto bg-background relative" data-tour="email-list">
         {/* Loading overlay */}
         {isLoading && emails.length > 0 && (
           <div className="absolute inset-0 bg-background/50 z-10 flex items-center justify-center animate-in fade-in duration-150">