C-01: sync_birthday_to_contacts now accepts (share_birthday, date_of_birth)
directly — no internal re-query, no stale-read risk with autoflush.
W-01: Eliminated redundant User/Settings SELECTs inside the service.
W-02: Removed scalar_one() on User query (no longer queries internally).
W-03: Settings router only syncs when share_birthday value actually changes.
S-02: Added logger.info with rowcount for observability.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>