feat(pr-sous-chef): use group-by-day to collapse run reports into one issue per day

[Copilot]

pr-sous-chef runs every 15 minutes and creates a new run-report issue each time, generating ~96 issues/day. Despite close-older-issues: true and labels: ["automation"], this floods the unlabeled triage queue with bot noise.

Changes

• pr-sous-chef.md: Add group-by-day: true to the create-issue safe-output config
• pr-sous-chef.lock.yml: Recompiled

create-issue:
  title-prefix: "[pr-sous-chef] "
  labels: ["automation"]
  expires: 3d
  close-older-issues: true
  group-by-day: true   # ← new

With group-by-day, the first run of each UTC day creates one labeled issue; all subsequent same-day runs append their stats as comments on that issue. Combined with close-older-issues, at most one open run-report issue exists at any time.