Scoped API keys with per-mailbox permissions

Features

• Scoped API keys with per-mailbox permissions
• Per-mailbox settings tab for managing individual mailbox configuration
• Templates browse and preview page
• Improved sent email list with delivery status icons and detail panel
• Pagination across all list views in the portal
• Sent emails now linked to conversation threads
• Sent tab sorted by latest thread activity
• Default mailbox auto-created on signup (tenant-wide inbox removed)

Fixes

• Fixed replies not appearing in the portal sent tab and inbox
• Fixed outbound messages missing email body content in threads
• Fixed flagged emails pagination and broken settings link
• Fixed docs site assets not loading when served behind portal rewrite
• Fixed sent query errors after adding thread support