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/bgm/src/schemas.ts

@@ -17,6 +17,9 @@ const stacking = z.object({
   limit: z.number().optional(),
   align: z.enum(['start', 'end', 'center']).optional(),
   steps: z.number().optional(),
+  tilt: z.number().optional(),
+  zStart: z.number().optional(),
+  zEnd: z.number().optional(),
 });
 
 const route = z.object({

packages/bgm/src/types.ts

@@ -107,6 +107,20 @@ export interface Stacking {
   align?: 'start' | 'end' | 'center';
   /** Maximum parts per curve length unit; defaults to `1`. */
   steps?: number;
+  /**
+   * Rotation in radians per shown part about the card's local Y (long) axis.
+   * Each part tilts `tilt` more than the previous, fanning the stack so its
+   * edges stay visible. Works with or without a `curve`.
+   */
+  tilt?: number;
+  /**
+   * Height (surface-normal) in mm at the start of the `curve`. The stack
+   * ramps linearly to `zEnd` across its span, lifting it in 3D. Requires a
+   * `curve`.
+   */
+  zStart?: number;
+  /** Height (surface-normal) in mm at the end of the `curve`. */
+  zEnd?: number;
 }
 
 /** How a surface is mounted. `kind` selects the mount type. */