fix(cron): accept bare duration units like 'hour' in schedule parsing - #97783

Fixes the schedule-parser/UI mismatch where "every hour" (advertised as a valid example) errors with Invalid duration: 'hour', while "every 1h" works.

Root cause

cron/jobs.py parse_duration() matched re.match(r'^(\d+)\s*(...)$') — a leading digit was mandatory. parse_schedule("every hour") strips "every " → "hour" → parse_duration("hour") failed the regex and raised. Bare-unit phrases like "hour" / "day" had no way to parse.

Fix

Made the leading number optional, defaulting to 1 when absent:

match = re.match(r'^(\d*)\s*(m|min|...|hour|hours|d|day|days)$', s)
value = int(match.group(1)) if match.group(1) else 1

Now "hour" → 60, "day" → 1440, "min" → 1, and existing forms ("30m", "2h", "1d", "every 2h") are unchanged.

Validation

• parse_duration("hour") → 60; "day" → 1440; "min" → 1.
• parse_schedule("every hour") → {kind: interval, minutes: 60}.
• Existing "30m", "2h", "1d", "every 2h", "every 30m" all unchanged.