Closes#45.
Two new server-side aggregates in computeStats(), same JS-bucketing
approach as the existing by_day: by_hour (localHourBucket — literal clock
time, no business-day rollover, feeds a left-to-right timeline) and
by_hour_of_day (localHourOfDay — every day's hour 0-23 summed together,
zero-filled to a full 24-entry axis so a quiet hour reads as zero, not a
missing data point).
Client: two more revenue charts on /stats — 'Umsatz nach Stunde' (timeline)
and 'Umsatz nach Tageszeit' (pattern). Revenue only, not also a tx-count
variant, to keep the page from growing a chart per metric per granularity.
Build clean both sides. Manually verified by_hour_of_day returns all 24
zero-filled buckets against a fresh DB.
6c2a938b91