Reports: scheduled email digests (weekly/monthly) actually send

Problem: email-reports store config but nothing sends them (audit).

Scope (Fathom-style): a scheduled job renders + emails the digest per configured frequency.

Done when: subscribers receive the digest on schedule.

Done in afe537f: the email-digests job on the #90 runtime sends each email-report on its daily/weekly/monthly schedule (lastSent-gated) with the period's pageview summary. Verified live. (Commit message mislabeled this as #93; #93's alert-evaluation is covered by the error-alerts job in 5317031/#80.)