DateType pattern isn’t anchored #283

JSON Schema pattern matches anywhere in the string, so "junk2026-11-09junk" validates, and so does "2026-13-45". The fix is ^…$. Time-zone offsets (+01:00, Z) currently pass only because of the missing anchor, so the anchored pattern should allow them deliberately, along with fractional seconds. Or it could just use format: date/date-time.