Reworks the Captain assistant "hours saved" metric so it produces a
believable number. It previously multiplied assistant reply count by
customer reply-wait time, which inflated the figure into the millions of
hours. It now estimates saved time as replies × a fixed ~2 min per-reply
effort assumption. On the overview card the value renders in days once
it passes 100 hours, and the label/hint copy was updated to match.
## How to test
1. Open the Captain assistant overview page.
2. Check the "Time saved" card shows a sensible value (hours, or days
past 100h).
3. Hover the hint and confirm it reflects the per-reply estimate.
