feat(catalog): class template editing

Templates were delete-and-recreate only. Adds PUT
/v1/catalog/class-templates/{id} across repository, service (sharing
the create-time validation), route, spec, and client; the classes tab
gets a pencil action that loads the row into the form with a
save/cancel affordance.

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

@@ -640,3 +640,43 @@ func TestCancelBookingPromotesWaitlist(t *testing.T) {
 		t.Fatalf("expected second waiter promoted, got %q", booking.Status)
 	}
 }
+
+func TestUpdateClassTemplate(t *testing.T) {
+	repo := db.NewMemoryRepository()
+	svc := newCatalogService(repo)
+	ctx := context.Background()
+
+	created, err := svc.CreateClassTemplate(ctx, owner, domain.UpsertClassTemplateRequest{
+		Title: "Yin Yoga", DurationMinutes: 75, Capacity: 10,
+	})
+	if err != nil {
+		t.Fatalf("create template: %v", err)
+	}
+
+	updated, err := svc.UpdateClassTemplate(ctx, owner, created.ID, domain.UpsertClassTemplateRequest{
+		Title: "Yin Yoga (večer)", DurationMinutes: 90, Capacity: 12,
+	})
+	if err != nil {
+		t.Fatalf("update template: %v", err)
+	}
+	if updated.Title != "Yin Yoga (večer)" || updated.DurationMinutes != 90 || updated.Capacity != 12 {
+		t.Fatalf("unexpected updated template: %+v", updated)
+	}
+
+	if _, err := svc.UpdateClassTemplate(ctx, owner, created.ID, domain.UpsertClassTemplateRequest{
+		Title: "", DurationMinutes: 90, Capacity: 12,
+	}); !errors.Is(err, ErrInvalidInput) {
+		t.Fatalf("expected ErrInvalidInput, got %v", err)
+	}
+	stranger := domain.Principal{Subject: "someone-else", Role: "staff"}
+	if _, err := svc.UpdateClassTemplate(ctx, stranger, created.ID, domain.UpsertClassTemplateRequest{
+		Title: "X", DurationMinutes: 60, Capacity: 5,
+	}); !errors.Is(err, ErrTenantMembership) {
+		t.Fatalf("expected ErrTenantMembership, got %v", err)
+	}
+	if _, err := svc.UpdateClassTemplate(ctx, owner, "00000000-0000-0000-0000-000000000099", domain.UpsertClassTemplateRequest{
+		Title: "X", DurationMinutes: 60, Capacity: 5,
+	}); !errors.Is(err, ErrClassTemplateNotFound) {
+		t.Fatalf("expected ErrClassTemplateNotFound, got %v", err)
+	}
+}