fix: skip recordDigestSent when RESEND_API_KEY absent (closes #2415)

[Rudrasamadhiya]

When RESEND_API_KEY is absent, sendEmail previously returned { ok: true } which caused recordDigestSent to be called, advancing last_digest_sent_at even though no email was actually sent. On the next cron run, these users would be silently skipped until the next weekly window.

This PR adds a skipped flag to the sendEmail return type so the cron handler can detect when the email step was a no-op and skip the timestamp update accordingly.

Changes

• Added skipped?: boolean to sendEmail return type
• • Return { ok: true, skipped: true } when API key is missing
• • Guard recordDigestSent call with !result.skipped
    Closes [BUG] Weekly digest cron treats missing RESEND_API_KEY as a successful send, consuming the 6-day cooldown with no email sent #2415

[github-actions]

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[Priyanshu-byte-coder]

This PR has merge conflicts with the current main branch. Please rebase or merge main into your branch to resolve the conflicts, then push the updated branch. Once conflicts are resolved, this PR will be merged.

git fetch origin main
git merge origin/main
# resolve conflicts
git push

[Priyanshu-byte-coder]

This PR has merge conflicts with main. Please rebase or resolve conflicts and push again.