feat: scheduled report digests + per-session capacity (M33)

POST /v1/internal/jobs/reports/dispatch emails each tenant owner a
trailing-window digest (bookings, revenue, per-service and per-staff
breakdown) localized to the tenant locale; zero-activity tenants are
skipped. Metrics cores extracted to tenant-scoped variants so the job
needs no principal.

PATCH /v1/catalog/class-sessions/:id sets a session's seat count with
a confirmed-bookings floor — shrinking below it needs allowOverCapacity,
matching the waitlist-promotion convention. Session rows gain an inline
capacity editor with an overbook confirm state.

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

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

apps/backend/internal/catalog/service_test.go

@@ -993,3 +993,61 @@ func TestUpdateClassScheduleWithoutCascade(t *testing.T) {
 		}
 	}
 }
+
+func TestUpdateClassSessionCapacityFloor(t *testing.T) {
+	repo := db.NewMemoryRepository()
+	svc := newCatalogService(repo)
+	ctx := context.Background()
+	tenantID := "5d6b3551-0a3e-4b86-bdf0-e9df20a47148"
+
+	session, err := repo.CreateClassSession(ctx, db.CreateClassSessionParams{
+		TenantID:   tenantID,
+		TemplateID: "d13fe5fd-727f-4d69-bfd8-47f1b92a2cf7",
+		StartsAt:   time.Now().UTC().Add(48 * time.Hour),
+		EndsAt:     time.Now().UTC().Add(49 * time.Hour),
+		Capacity:   4,
+	})
+	if err != nil {
+		t.Fatalf("create session: %v", err)
+	}
+	for _, name := range []string{"A", "B", "C"} {
+		if _, err := repo.CreateBooking(ctx, db.CreateBookingParams{
+			TenantID:       tenantID,
+			ClassSessionID: &session.ID,
+			BookingMode:    "class",
+			CustomerName:   name,
+			CustomerEmail:  name + "@example.com",
+			StartsAt:       session.StartsAt,
+			EndsAt:         session.EndsAt,
+			Status:         "confirmed",
+			Reference:      "BK-CAP-" + name,
+		}); err != nil {
+			t.Fatalf("seed booking %s: %v", name, err)
+		}
+	}
+
+	// Shrinking to 2 with 3 confirmed seats → conflict without override.
+	cap2 := 2
+	if _, err := svc.UpdateClassSession(ctx, owner, session.ID, domain.UpdateClassSessionRequest{Capacity: &cap2}); !errors.Is(err, ErrCapacityBelowBooked) {
+		t.Fatalf("expected ErrCapacityBelowBooked, got %v", err)
+	}
+	// With override it applies.
+	updated, err := svc.UpdateClassSession(ctx, owner, session.ID, domain.UpdateClassSessionRequest{Capacity: &cap2, AllowOverCapacity: true})
+	if err != nil {
+		t.Fatalf("override update: %v", err)
+	}
+	if updated.Capacity != 2 || updated.BookedCount != 3 {
+		t.Fatalf("expected capacity=2 booked=3, got %d/%d", updated.Capacity, updated.BookedCount)
+	}
+	// Growing always works.
+	cap8 := 8
+	updated, err = svc.UpdateClassSession(ctx, owner, session.ID, domain.UpdateClassSessionRequest{Capacity: &cap8})
+	if err != nil || updated.Capacity != 8 {
+		t.Fatalf("grow update: %v cap=%d", err, updated.Capacity)
+	}
+	// Validation floor.
+	cap0 := 0
+	if _, err := svc.UpdateClassSession(ctx, owner, session.ID, domain.UpdateClassSessionRequest{Capacity: &cap0}); !errors.Is(err, ErrInvalidInput) {
+		t.Fatalf("expected ErrInvalidInput for capacity 0, got %v", err)
+	}
+}