fix: activity chart uses rolling chronological windows (real dates), not cyclical

Day/Week/Month/Year now show the anchor day hour-by-hour, the last 7 days, the
last 30 days, and the last 12 months — anchored to the period end (else now), in
real date order. Replaces the cyclical hour-of-day/weekday/day-of-month/month
buckets, which left future days empty and ordered the weekend after Monday.

internal/qso/stats.go

@@ -163,12 +163,13 @@ type Stats struct {
 	ByYear      []Bucket `json:"by_year"`  // chronological
 	ByMonth     []Bucket `json:"by_month"` // "YYYY-MM", chronological
 
-	// Cyclical activity distributions (UTC), for the "activity over time" chart's
-	// day/week/month/year granularity selector.
-	ByHour    []Bucket `json:"by_hour"`     // hour of day 00..23
-	ByDOW     []Bucket `json:"by_dow"`      // day of week Mon..Sun
-	ByDOM     []Bucket `json:"by_dom"`      // day of month 1..31
-	ByMonthYr []Bucket `json:"by_month_yr"` // month Jan..Dec
+	// Rolling chronological activity windows (UTC), anchored to the newest QSO, for
+	// the "activity over time" chart's day/week/month/year granularity selector.
+	// Real dates in order (empty buckets are real, just zero) — no cyclical wrap.
+	ByHour    []Bucket `json:"by_hour"`     // the newest QSO's day, hour by hour (00..23)
+	ByDay7    []Bucket `json:"by_day7"`     // the last 7 days ending at the newest QSO
+	ByDay30   []Bucket `json:"by_day30"`    // the last 30 days
+	ByMonth12 []Bucket `json:"by_month12"`  // the last 12 months
 
 	// ── Period / contest metrics ──
 	// Meaningful only over a WINDOW: "12 QSO/h" across seventeen years says
@@ -476,40 +477,55 @@ func (r *Repo) Stats(ctx context.Context, from, to time.Time, contestID string,
 	s.ByMonth = fillMonths(monthC, first, last)
 
 	s.periodMetrics(times, from, to, first, last)
-	s.timeDistributions(times)
+	// Anchor the rolling activity windows to the period end when filtered, else to
+	// now (so "week" is the last 7 days ending today, like the operator expects).
+	ref := to
+	if ref.IsZero() {
+		ref = time.Now()
+	}
+	s.recentSeries(times, ref)
 	s.ensureNonNil()
 
 	return s, nil
 }
 
-// timeDistributions builds the cyclical activity buckets (hour-of-day, day-of-week,
-// day-of-month, month-of-year) from the dated QSOs, in UTC. Each is a fixed-length
-// series so the chart axis is stable even for empty slots.
-func (s *Stats) timeDistributions(times []entry) {
+// recentSeries builds the rolling chronological activity windows for the chart's
+// day/week/month/year selector, in UTC and anchored to `ref` (the period end when
+// filtered, else now). Real dates in order — today and the days before it — so the
+// axis reads chronologically and empty days are just zero, not misordered/wrapped.
+func (s *Stats) recentSeries(times []entry, ref time.Time) {
+	ref = ref.UTC()
+	day0 := time.Date(ref.Year(), ref.Month(), ref.Day(), 0, 0, 0, 0, time.UTC) // midnight of the anchor day
 	hour := make([]int, 24)
-	dow := make([]int, 7) // 0 = Monday
-	dom := make([]int, 31)
-	moy := make([]int, 12)
+	daily := map[string]int{}
+	monthly := map[string]int{}
 	for _, e := range times {
 		t := e.t.UTC()
-		hour[t.Hour()]++
-		dow[(int(t.Weekday())+6)%7]++ // shift Sunday(0) → 6 so Monday is first
-		if d := t.Day(); d >= 1 && d <= 31 {
-			dom[d-1]++
+		if t.Year() == ref.Year() && t.YearDay() == ref.YearDay() {
+			hour[t.Hour()]++
 		}
-		moy[int(t.Month())-1]++
+		daily[t.Format("2006-01-02")]++
+		monthly[t.Format("2006-01")]++
 	}
+	// Day: the anchor day, hour by hour.
 	for h := 0; h < 24; h++ {
-		s.ByHour = append(s.ByHour, Bucket{Key: fmt.Sprintf("%02d", h), Count: hour[h]})
+		s.ByHour = append(s.ByHour, Bucket{Key: fmt.Sprintf("%02dh", h), Count: hour[h]})
 	}
-	for i, n := range []string{"Mon", "Tue", "Wed", "Thu", "Fri", "Sat", "Sun"} {
-		s.ByDOW = append(s.ByDOW, Bucket{Key: n, Count: dow[i]})
+	// Week: the last 7 days ending today (today is last). Label = weekday + day.
+	for i := 6; i >= 0; i-- {
+		d := day0.AddDate(0, 0, -i)
+		s.ByDay7 = append(s.ByDay7, Bucket{Key: d.Format("Mon 2"), Count: daily[d.Format("2006-01-02")]})
 	}
-	for d := 1; d <= 31; d++ {
-		s.ByDOM = append(s.ByDOM, Bucket{Key: fmt.Sprintf("%d", d), Count: dom[d-1]})
+	// Month: the last 30 days.
+	for i := 29; i >= 0; i-- {
+		d := day0.AddDate(0, 0, -i)
+		s.ByDay30 = append(s.ByDay30, Bucket{Key: d.Format("2/1"), Count: daily[d.Format("2006-01-02")]})
 	}
-	for i, n := range []string{"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"} {
-		s.ByMonthYr = append(s.ByMonthYr, Bucket{Key: n, Count: moy[i]})
+	// Year: the last 12 months.
+	m0 := time.Date(ref.Year(), ref.Month(), 1, 0, 0, 0, 0, time.UTC)
+	for i := 11; i >= 0; i-- {
+		m := m0.AddDate(0, -i, 0)
+		s.ByMonth12 = append(s.ByMonth12, Bucket{Key: m.Format("Jan 06"), Count: monthly[m.Format("2006-01")]})
 	}
 }