Outbound email attachments support via Resend

Features

• Outbound email attachments support via Resend
• Catch-all mailbox routing for unmatched inbound emails
• Domains now automatically receive inbound email capabilities
• Storage usage and attachment management endpoints

Fixes

• Fixed thread matching so replies link to the correct conversation
• Fixed new inbound emails creating duplicate threads
• Fixed tenant resolution for shared-domain inbound emails
• Fixed Resend domain webhook handling for verification status syncing
• Fixed login token exchange to work reliably behind proxies
• Each outbound send now correctly creates its own thread