Add a "new regressions" column to the listing pages

## Summary

Add a new column showing the number of new regressions on the Trees, Hardware, and Labs listing pages. Today these pages show status aggregates per row but give no visibility into regressions without opening a detail page.

## Motivation

- Regressions are the highest-signal event for maintainers; a raw fail count doesn't distinguish a long-standing known failure from something that just broke.
- Surfacing regressions at the listing level speeds up triage — spot regressing trees/hardware/labs at a glance instead of drilling into each one.

## Proposed change

Add a "New regressions" column, showing the count of new regressions per row, to each listing page. Tracked per page as sub-issues:

- [ ] Hardware listing
- [ ] Trees listing
- [ ] Labs listing

## Acceptance criteria

- [ ] Trees, Hardware, and Labs listings each show a new-regressions column with an accurate count.
- [ ] No noticeable increase in listing load time from the added data.

Start by locating the Trees, Hardware, and Labs listing page entry points and reviewing how their existing status aggregates are loaded. Add and verify a “New regressions” column for each page, confirming counts are accurate and that listing load time does not noticeably increase.

Written by the indexing model from the issue text.