feat(dashboard): real business metrics with week-over-week trends

Dashboard KPIs were three flat counters with no trend data — the cards
rendered a neutral dash where the design intends movement indicators.
Summary now queries three trailing windows and emits four KPIs with
real deltas: bookings this week, completed (new CompletedCount metric
in both repositories), cancellations, and utilization in percentage
points. KPI labels localize in the frontend via a code-to-key map so
Czech operators no longer see English labels on live data.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/bookings/service.go

@@ -569,6 +569,14 @@ func (s *Service) DashboardSummary(ctx context.Context, principal domain.Princip
 	if err != nil {
 		return domain.DashboardSummary{}, err
 	}
+	previousMetrics, err := s.repo.GetDashboardMetrics(ctx, membership.Tenant.ID, now.AddDate(0, 0, -7), now)
+	if err != nil {
+		return domain.DashboardSummary{}, err
+	}
+	priorMetrics, err := s.repo.GetDashboardMetrics(ctx, membership.Tenant.ID, now.AddDate(0, 0, -14), now.AddDate(0, 0, -7))
+	if err != nil {
+		return domain.DashboardSummary{}, err
+	}
 	upcomingRecords, err := s.repo.ListBookingsByTenantBetween(ctx, membership.Tenant.ID, now, weekEnd)
 	if err != nil {
 		return domain.DashboardSummary{}, err
@@ -614,9 +622,10 @@ func (s *Service) DashboardSummary(ctx context.Context, principal domain.Princip
 		PublicBookingURL: "/book/" + membership.Tenant.Slug,
 		SetupCompletion:  setupCompletion(brandName, len(locationNames), len(serviceNames), len(staffNames), scheduleCount),
 		KPIs: []domain.DashboardKPI{
-			{Code: "bookings_this_week", Label: "Bookings this week", Value: fmt.Sprintf("%d", metrics.BookingsCount)},
-			{Code: "cancellations", Label: "Cancellations", Value: fmt.Sprintf("%d", metrics.CancellationsCount)},
-			{Code: "utilization", Label: "Utilization", Value: fmt.Sprintf("%d%%", metrics.UtilizationPercent)},
+			dashboardKPI("bookings_this_week", "Bookings this week", metrics.BookingsCount, previousMetrics.BookingsCount, ""),
+			dashboardKPI("completed", "Completed", previousMetrics.CompletedCount, priorMetrics.CompletedCount, ""),
+			dashboardKPI("cancellations", "Cancellations", metrics.CancellationsCount, previousMetrics.CancellationsCount, ""),
+			dashboardKPI("utilization", "Utilization", metrics.UtilizationPercent, previousMetrics.UtilizationPercent, "%"),
 		},
 		UpcomingBookings: upcoming,
 		AllBookings:      allBookings,
@@ -909,3 +918,20 @@ func reminderSchedule(startsAt time.Time) (time.Time, bool) {
 		return time.Time{}, false
 	}
 }
+
+func dashboardKPI(code, label string, current int, previous int, suffix string) domain.DashboardKPI {
+	delta := current - previous
+	change := "0"
+	trend := "neutral"
+	if delta > 0 {
+		change = fmt.Sprintf("+%d", delta)
+		trend = "up"
+	} else if delta < 0 {
+		change = fmt.Sprintf("%d", delta)
+		trend = "down"
+	}
+	if suffix != "" && change != "0" {
+		change += suffix
+	}
+	return domain.DashboardKPI{Code: code, Label: label, Value: fmt.Sprintf("%d%s", current, suffix), Change: change, Trend: trend}
+}