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.

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

apps/backend/internal/db/repository.go

@@ -394,6 +394,7 @@ type DashboardMetrics struct {
 	BookingsCount      int
 	CancellationsCount int
 	UtilizationPercent int
+	CompletedCount     int
 }
 
 type ReminderJobParams struct {
@@ -1452,6 +1453,9 @@ func (r *MemoryRepository) GetDashboardMetrics(_ context.Context, tenantID strin
 		}
 		if booking.Status == "confirmed" {
 			metrics.UtilizationPercent++
+			if booking.EndsAt.Before(time.Now().UTC()) {
+				metrics.CompletedCount++
+			}
 		}
 	}
 	if metrics.BookingsCount == 0 {