Support inbox polish: helpdesk layout and message previews

Shipped a production-grade support inbox polish pass inspired by leading help desks.

Delivered:

• Three-pane inbox layout with ticket list, conversation thread, and details sidebar
• Avatars and clearer message bubbles for easier conversation scanning
• Ticket properties panel for status, priority, queue, and assignee
• Friendlier empty states, composer copy, and threading affordances
• Latest-message previews in the ticket list so agents can triage without opening every ticket

Release:

• GitHub: pushed to master at commit 8cb248a
• Production: deployed to https://hollahoop.app