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/placement.tsx

@@ -17,20 +17,22 @@ export function PartPlacement({ pkg, placement }: { pkg: Package; placement: Pla
   const part = pkg.parts.get(piece.split(':').slice(1).join(':'));
   if (!part) return null;
 
-  const { x, y, rotation } = useStacking(route.stacking, index, stackSize);
+  const { x, y, rotation, z, tilt } = useStacking(route.stacking, index, stackSize);
 
   // Route anchors and stacking offsets are in mm; convert to world units so
-  // parts land on the (world-scaled) surface.
+  // parts land on the (world-scaled) surface. `z` raises the part along the
+  // surface normal (world +Y); `tilt` fans it about its local Y (long) axis.
   const anchorX = ((candidate?.x ?? route.x ?? 0) + x) * MM_TO_WORLD;
   const anchorY = ((candidate?.y ?? route.y ?? 0) + y) * MM_TO_WORLD;
+  const anchorZ = z * MM_TO_WORLD;
   const anchorRotation = (candidate?.rotation ?? route.rotation ?? 0) + rotation;
 
   return (
-    <group position={[anchorX, 0, anchorY]} rotation={[0, anchorRotation, 0]}>
+    <group position={[anchorX, anchorZ, anchorY]} rotation={[0, anchorRotation, 0]}>
       {/* The part mesh extrudes along +Z; lay it flat so its face points up. */}
-      <group rotation={[-Math.PI / 2, 0, 0]}>
+      <group rotation={[-Math.PI / 2, 0, tilt]}>
         <PartView part={part} baseUrl={part.baseUrl} />
       </group>
     </group>
   );
-}
+}