fix(tabletop): tilt cards uniformly about the y axis

Apply the same tilt to every stacked part and rotate it about its local
Y axis instead of Z. Default tilt to 1 degree when a stacking strategy
is present, and arc the poker deck along the surface's bottom edge.

packages/tabletop/src/stacking.test.ts

@@ -46,7 +46,8 @@ describe('pointAt', () => {
 describe('stackingOffset', () => {
   it('returns no offset without a curve', () => {
     expect(stackingOffset(undefined, 0, 3)).toBe(NO_OFFSET);
-    expect(stackingOffset({ limit: 5 }, 0, 3)).toBe(NO_OFFSET);
+    // A stacking strategy defaults to a 1° tilt, so it's not the identity.
+    expect(stackingOffset({ limit: 5 }, 0, 3)).toEqual({ x: 0, y: 0, rotation: 0, z: 0, tilt: 1 });
   });
 
   it('spreads parts evenly along a straight curve', () => {
@@ -86,12 +87,12 @@ describe('stackingOffset', () => {
     expect(offset.x).toBeCloseTo(25);
   });
 
-  it('tilts each part without a curve', () => {
+  it('tilts every part the same amount without a curve', () => {
     const offset = stackingOffset({ tilt: 0.1 }, 2, 3);
-    expect(offset).toEqual({ x: 0, y: 0, rotation: 0, z: 0, tilt: 0.2 });
+    expect(offset).toEqual({ x: 0, y: 0, rotation: 0, z: 0, tilt: 0.1 });
   });
 
-  it('tilts parts along the curve', () => {
+  it('tilts every part the same amount along the curve', () => {
     const offset = stackingOffset({ curve: 'M 0 0 L 100 0', tilt: 0.1 }, 1, 3);
     expect(offset.x).toBeCloseTo(50);
     expect(offset.tilt).toBeCloseTo(0.1);
@@ -113,7 +114,7 @@ describe('stackingOffset', () => {
     expect(last.z).toBeCloseTo(40);
   });
 
-  it('returns no offset without a curve, tilt, or z ramp', () => {
-    expect(stackingOffset({ limit: 5 }, 0, 3)).toBe(NO_OFFSET);
+  it('returns no offset without a stacking strategy', () => {
+    expect(stackingOffset(undefined, 0, 3)).toBe(NO_OFFSET);
   });
 });