Add Forward button to emails with attachment support

[UmakanthKaspa]

What does this do?

Adds a "Forward" button next to Reply and Reply All buttons in email view. When you click Forward, it
opens the email composer with:

• Empty recipient fields (so you can choose who to forward to)
• Original email's attachments automatically copied
• Subject prefixed with "Fw:"
• Original email content shown as quoted text
• Cursor positioned at the top so you can type your message

Why is this useful?

Users can now forward emails to other people, just like in Gmail or Outlook.

How does it work?

1. Click the Forward button on any email
2. Email composer opens with attachments already included
3. Add recipients and type your message
4. Send

The forwarded email includes all original attachments, making it easy to share important files with
others.

Fixes

Closes #1359

Testing

Tested with:

• ✅ Forwarding emails with attachments
• ✅ Forwarding emails without attachments
• ✅ Cursor starts at correct position (above quoted content)
• ✅ Subject gets "Fw:" prefix
• ✅ Attachments can be removed before sending