Configurable grid + snap-to-grid in the layout system (#45)

Closes #44. Two independent grids (garden + per-bed), each with a size and a snap toggle; snapping defaults off. See PR #45 for details.

Co-authored-by: Steve Dudenhoeffer <[email protected]>

internal/service/gardens_test.go

@@ -57,6 +57,7 @@ func TestCreateGardenValidation(t *testing.T) {
 		{Name: "X", WidthCM: math.NaN()},                             // NaN slips past naive < / >
 		{Name: "X", HeightCM: math.Inf(1)},                           // +Inf
 		{Name: "X", WidthCM: math.SmallestNonzeroFloat64},            // subnormal, > 0 but < 1 cm
+		{Name: "X", GridSizeCM: maxGardenCM + 1},                     // grid over the cap
 	}
 	for i, in := range cases {
 		if _, err := s.CreateGarden(context.Background(), owner, in); !errors.Is(err, domain.ErrInvalidInput) {
@@ -70,6 +71,51 @@ func TestCreateGardenValidation(t *testing.T) {
 	}
 }
 
+func TestGardenGridSettings(t *testing.T) {
+	s := newTestService(t, openConfig())
+	owner := seedUser(t, s, "[email protected]")
+	ctx := context.Background()
+
+	// An omitted grid size lands the default; snap defaults off.
+	g, err := s.CreateGarden(ctx, owner, GardenInput{Name: "G"})
+	if err != nil {
+		t.Fatalf("CreateGarden: %v", err)
+	}
+	if g.GridSizeCM != defaultGardenGridCM {
+		t.Errorf("grid = %v, want default %d", g.GridSizeCM, defaultGardenGridCM)
+	}
+	if g.SnapToGrid {
+		t.Error("snap should default off")
+	}
+
+	// An update sets an explicit grid and turns snap on; both persist.
+	up, err := s.UpdateGarden(ctx, owner, g.ID, GardenInput{
+		Name: "G", WidthCM: g.WidthCM, HeightCM: g.HeightCM, UnitPref: g.UnitPref,
+		GridSizeCM: 25, SnapToGrid: true,
+	}, g.Version)
+	if err != nil {
+		t.Fatalf("UpdateGarden: %v", err)
+	}
+	got, err := s.GetGarden(ctx, owner, g.ID)
+	if err != nil {
+		t.Fatalf("GetGarden: %v", err)
+	}
+	if got.GridSizeCM != 25 || !got.SnapToGrid {
+		t.Errorf("persisted grid=%v snap=%v, want 25/true", got.GridSizeCM, got.SnapToGrid)
+	}
+
+	// An update omitting the grid size (0) is re-defaulted, not stored as 0.
+	up2, err := s.UpdateGarden(ctx, owner, g.ID, GardenInput{
+		Name: "G", WidthCM: g.WidthCM, HeightCM: g.HeightCM, UnitPref: g.UnitPref,
+	}, up.Version)
+	if err != nil {
+		t.Fatalf("UpdateGarden(reset): %v", err)
+	}
+	if up2.GridSizeCM != defaultGardenGridCM || up2.SnapToGrid {
+		t.Errorf("after omit grid=%v snap=%v, want default/false", up2.GridSizeCM, up2.SnapToGrid)
+	}
+}
+
 func TestListGardensOwnedOnly(t *testing.T) {
 	s := newTestService(t, openConfig())
 	alice := seedUser(t, s, "[email protected]")