feat(tabletop): add tilt and zStart/zEnd stacking options

Replace the per-part lift with a local Y-axis tilt that fans the stack,
and add zStart/zEnd to ramp the stack's height across the curve so it
arches in 3D. Update the poker deck and docs accordingly.

packages/tabletop/src/stacking.test.ts

@@ -85,4 +85,35 @@ describe('stackingOffset', () => {
     const offset = stackingOffset({ curve: 'M 0 0 L 100 0', steps: 4 }, 1, 3);
     expect(offset.x).toBeCloseTo(25);
   });
+
+  it('tilts each part 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 });
+  });
+
+  it('tilts parts 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);
+  });
+
+  it('tilts only the shown parts', () => {
+    // limit 2 shows indices 0,1; index 2 is dropped.
+    expect(stackingOffset({ tilt: 0.1, limit: 2 }, 2, 4)).toBe(NO_OFFSET);
+    expect(stackingOffset({ tilt: 0.1, limit: 2 }, 1, 4).tilt).toBeCloseTo(0.1);
+  });
+
+  it('ramps z from zStart to zEnd across the curve', () => {
+    // 3 parts on a 100-long curve: u = 0, 0.5, 1. z ramps 0 -> 40.
+    const first = stackingOffset({ curve: 'M 0 0 L 100 0', zStart: 0, zEnd: 40 }, 0, 3);
+    const mid = stackingOffset({ curve: 'M 0 0 L 100 0', zStart: 0, zEnd: 40 }, 1, 3);
+    const last = stackingOffset({ curve: 'M 0 0 L 100 0', zStart: 0, zEnd: 40 }, 2, 3);
+    expect(first.z).toBeCloseTo(0);
+    expect(mid.z).toBeCloseTo(20);
+    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);
+  });
 });