Add estimated hours field to tickets for workload planning

[asamawi]

Problem

When managing a support team (or working solo), there's no way to answer the question: "How many hours of work are sitting in our open tickets?"

Without this, you can't tell if you have 5 hours of work in the queue or 50. You only know the count of open tickets — but a password reset (5 minutes) and a server migration (6 hours) look the same.

Proposed Solution

Add a built-in estimated_hours field to HD Ticket (Float, optional).

• When it's set: An agent fills it in when they first review the ticket — a rough estimate of how long the work will take (e.g., 0.5, 1, 4 hours)
• Where it's visible: Ticket detail view, and optionally in list and Kanban views
• How it's used: Teams can sum estimated hours across open tickets to see total workload in hours, not just ticket count

Example

Ticket	Priority	Estimated Hours
Printer not working	Medium	0.5
Email migration	High	4
Password reset	Low	0.25
Server crash investigation	Urgent	3
Total workload		7.75 hours

Knowing "we have 7.75 hours of work queued" is far more useful than "we have 4 open tickets."

Additional Context

This pairs naturally with time tracking (#2351) — estimated hours tells you what's coming, actual hours tells you what happened. But estimated hours has standalone value even without time tracking.