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/bookings.go

@@ -179,13 +179,15 @@ func (r *PGRepository) GetDashboardMetrics(ctx context.Context, tenantID string,
 					/ NULLIF(COUNT(*) FILTER (WHERE starts_at >= $2 AND starts_at < $3), 0)
 				),
 				0
-			)::integer AS utilization_percent
+			)::integer AS utilization_percent,
+			COUNT(*) FILTER (WHERE starts_at >= $2 AND starts_at < $3 AND status = 'confirmed' AND ends_at < now()) AS completed_count
 		FROM bookings
 		WHERE tenant_id = $1
 	`, tenantID, startsAt, endsAt).Scan(
 		&metrics.BookingsCount,
 		&metrics.CancellationsCount,
 		&metrics.UtilizationPercent,
+		&metrics.CompletedCount,
 	)
 	return metrics, err
 }