stats: add hourly views — continuous timeline + hour-of-day pattern

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.

server/src/routes/admin.ts

@@ -1,6 +1,6 @@
 import type { FastifyInstance, FastifyReply, FastifyRequest } from 'fastify';
 import type { DB } from '../db.js';
-import { businessDay, formatLocal, parseDbTime } from '../time.js';
+import { businessDay, formatLocal, localHourBucket, localHourOfDay, parseDbTime } from '../time.js';
 import { createHash, randomBytes, timingSafeEqual } from 'node:crypto';
 import { sendProblem } from '../problem-details.js';
 
@@ -130,6 +130,51 @@ function computeStats(db: DB) {
   // /stats "recent days" table), where the most recent day belongs on top.
   const byDay = [...dayMap.values()].sort((a, b) => b.day.localeCompare(a.day));
 
+  // Two hourly views for #45 ("why not both" — the continuous timeline and
+  // the hour-of-day pattern answer different questions, see the issue
+  // comment). Same shape as dayMap's aggregates, same JS-bucketing
+  // reasoning, just keyed differently: localHourBucket() is literal clock
+  // time (no business-day rollover — the point is "when did this happen"),
+  // localHourOfDay() collapses every day onto a 0-23 axis.
+  type HourAgg = { tx_count: number; paid_cents: number; crew_count: number; pfand_returns: number };
+  function bumpHourAgg(agg: HourAgg, r: { total_cents: number; crew: number; pfand_returns: number }) {
+    agg.tx_count += 1;
+    if (r.crew) agg.crew_count += 1;
+    else agg.paid_cents += r.total_cents;
+    agg.pfand_returns += r.pfand_returns;
+  }
+
+  const hourMap = new Map<string, { hour: string } & HourAgg>();
+  const hourOfDayMap = new Map<number, { hour_of_day: number } & HourAgg>();
+  for (const r of txRows) {
+    const d = parseDbTime(r.created_at);
+
+    const hourKey = localHourBucket(d);
+    let hourAgg = hourMap.get(hourKey);
+    if (!hourAgg) {
+      hourAgg = { hour: hourKey, tx_count: 0, paid_cents: 0, crew_count: 0, pfand_returns: 0 };
+      hourMap.set(hourKey, hourAgg);
+    }
+    bumpHourAgg(hourAgg, r);
+
+    const hod = localHourOfDay(d);
+    let hodAgg = hourOfDayMap.get(hod);
+    if (!hodAgg) {
+      hodAgg = { hour_of_day: hod, tx_count: 0, paid_cents: 0, crew_count: 0, pfand_returns: 0 };
+      hourOfDayMap.set(hod, hodAgg);
+    }
+    bumpHourAgg(hodAgg, r);
+  }
+  // Oldest first, same reasoning as perDrinkByDay below — this feeds a
+  // left-to-right timeline chart.
+  const byHour = [...hourMap.values()].sort((a, b) => a.hour.localeCompare(b.hour));
+  // Full 0-23 axis, zero-filled — a bar chart with silently missing hours
+  // (e.g. no sales at 6am) reads as a data gap, not "zero", if the bucket
+  // is just absent.
+  const byHourOfDay = Array.from({ length: 24 }, (_, h) => hourOfDayMap.get(h) ?? {
+    hour_of_day: h, tx_count: 0, paid_cents: 0, crew_count: 0, pfand_returns: 0,
+  });
+
   // Per-day-per-drink sold quantity — the "trend over time" data #40 asked
   // for, on top of the all-time perDrink totals above. Same businessDay()
   // JS bucketing as byDay, for the same DST-correctness reason; joined
@@ -166,7 +211,14 @@ function computeStats(db: DB) {
     .sort((a, b) => a[0].localeCompare(b[0]))
     .map(([day, drinks]) => ({ day, drinks: [...drinks.values()].sort((a, b) => b.sold_qty - a.sold_qty) }));
 
-  return { totals, per_drink: perDrink, by_day: byDay, per_drink_by_day: perDrinkByDay };
+  return {
+    totals,
+    per_drink: perDrink,
+    by_day: byDay,
+    per_drink_by_day: perDrinkByDay,
+    by_hour: byHour,
+    by_hour_of_day: byHourOfDay,
+  };
 }
 
 export function registerAdminRoutes(app: FastifyInstance, db: DB) {