feat(metrics): per-staff performance view in dashboard

GET /v1/metrics/staff returns bookings, completed, cancelled,
utilization, and revenue per staff member over a trailing window
(default 30d, max 365d). Appointment bookings only — class sessions
have no staff assignment. All active staff appear, including
zero-booking rows.

Staff page gains a localized Performance panel; demo mode seeds
trailing-window bookings and matching metric rows.

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

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

apps/backend/internal/db/repository.go

@@ -146,6 +146,9 @@ type Repository interface {
 	// Activity feed
 	AppendActivityEvent(ctx context.Context, params ActivityEventParams) error
 	ListActivityEvents(ctx context.Context, tenantID string, limit int) ([]ActivityEventRecord, error)
+
+	// Staff metrics
+	GetStaffMetrics(ctx context.Context, tenantID string, from time.Time, to time.Time) ([]StaffMetricsRecord, error)
 }
 
 type TenantRecord struct {
@@ -302,6 +305,17 @@ type StaffFeedTokenRecord struct {
 	FeedToken   string
 }
 
+// StaffMetricsRecord is a per-staff aggregation of appointment bookings —
+// class bookings carry no staff_id and are excluded by design.
+type StaffMetricsRecord struct {
+	StaffID            string
+	BookingsCount      int
+	CancellationsCount int
+	CompletedCount     int
+	UtilizationPercent int
+	RevenueCents       int64
+}
+
 // ActivityEventRecord / ActivityEventParams back the per-tenant audit feed.
 type ActivityEventRecord struct {
 	ID         string
@@ -653,7 +667,9 @@ type PGRepository struct {
 
 func NewRepository(pools *Pools, demoMode bool) Repository {
 	if demoMode {
-		return NewMemoryRepository()
+		repo := NewMemoryRepository()
+		repo.seedDemoBookings()
+		return repo
 	}
 	if pools != nil && pools.App != nil {
 		return &PGRepository{pool: pools.App}
@@ -1574,6 +1590,34 @@ func (r *MemoryRepository) CreateBooking(_ context.Context, params CreateBooking
 	return created, nil
 }
 
+func (r *MemoryRepository) seedDemoBookings() {
+	now := time.Now().UTC()
+	serviceID := r.services[0].ID
+	staffID := r.staff[0].ID
+	locationID := r.locations[0].ID
+	seed := func(name, email, status string, startsAt time.Time) {
+		r.bookings = append(r.bookings, BookingRecord{
+			ID:            uuid.NewString(),
+			TenantID:      r.tenant.ID,
+			ServiceID:     &serviceID,
+			StaffID:       &staffID,
+			LocationID:    &locationID,
+			CustomerName:  name,
+			CustomerEmail: email,
+			StartsAt:      startsAt,
+			EndsAt:        startsAt.Add(time.Hour),
+			Status:        status,
+			Reference:     "BK-DEMO-" + uuid.NewString()[:8],
+			ManageToken:   uuid.NewString(),
+			CreatedAt:     startsAt.Add(-48 * time.Hour),
+		})
+	}
+	seed("Alice Johnson", "[email protected]", "confirmed", now.Add(-4*time.Hour))
+	seed("Bob Smith", "[email protected]", "confirmed", now.Add(-26*time.Hour))
+	seed("Carol White", "[email protected]", "confirmed", now.Add(-50*time.Hour))
+	seed("Alice Johnson", "[email protected]", "cancelled", now.Add(-74*time.Hour))
+}
+
 func (r *MemoryRepository) AppendWaitlistEntry(_ context.Context, _ WaitlistEntryParams) error {
 	r.waitlistSize++
 	return nil
@@ -1721,6 +1765,51 @@ func (r *MemoryRepository) GetDashboardMetrics(_ context.Context, tenantID strin
 	return metrics, nil
 }
 
+func (r *MemoryRepository) GetStaffMetrics(_ context.Context, tenantID string, startsAt time.Time, endsAt time.Time) ([]StaffMetricsRecord, error) {
+	servicePrices := make(map[string]int, len(r.services))
+	for _, service := range r.services {
+		servicePrices[service.ID] = service.PriceCents
+	}
+	byStaff := map[string]*StaffMetricsRecord{}
+	for _, booking := range r.bookings {
+		if booking.TenantID != tenantID || booking.StaffID == nil {
+			continue
+		}
+		if booking.StartsAt.Before(startsAt) || !booking.StartsAt.Before(endsAt) {
+			continue
+		}
+		rec := byStaff[*booking.StaffID]
+		if rec == nil {
+			rec = &StaffMetricsRecord{StaffID: *booking.StaffID}
+			byStaff[*booking.StaffID] = rec
+		}
+		rec.BookingsCount++
+		switch {
+		case booking.Status == "cancelled":
+			rec.CancellationsCount++
+		case booking.Status == "confirmed":
+			rec.UtilizationPercent++
+			if booking.EndsAt.Before(time.Now().UTC()) {
+				rec.CompletedCount++
+			}
+		}
+		if booking.Status != "cancelled" && booking.ServiceID != nil {
+			rec.RevenueCents += int64(servicePrices[*booking.ServiceID])
+		}
+	}
+	records := make([]StaffMetricsRecord, 0, len(byStaff))
+	for _, rec := range byStaff {
+		if rec.BookingsCount == 0 {
+			rec.UtilizationPercent = 0
+		} else {
+			rec.UtilizationPercent = int(float64(rec.UtilizationPercent) / float64(rec.BookingsCount) * 100)
+		}
+		records = append(records, *rec)
+	}
+	sort.SliceStable(records, func(i, j int) bool { return records[i].BookingsCount > records[j].BookingsCount })
+	return records, nil
+}
+
 func (r *MemoryRepository) GetSubscriptionSnapshot(_ context.Context, tenantID string) (BillingSnapshotRecord, error) {
 	if tenantID != r.tenant.ID {
 		return BillingSnapshotRecord{}, pgx.ErrNoRows