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.

docs/bgm-tabletop-plan.md

@@ -118,10 +118,12 @@ interface GameState {
 
 ### 7. Stacking (`stacking.ts`) ✅
 
-- `useStacking(route.stacking, index, stackSize)` → `{ offset, rotation }`.
+- `useStacking(route.stacking, index, stackSize)` → `{ x, y, rotation, z, tilt }`.
 - Implements the format's positioning process (`bgm-format.md` §4): step
   length from curve length / `max(steps, count-1)`, alignment (`start`/`end`/
   `center`), and `limit` (`0` all, `n` first n, `-n` last n).
+- `z` ramps linearly from `zStart` to `zEnd` across the curve's span; `tilt`
+  fans each shown part about its local Y (long) axis.
 - Curve length from an SVG path string (small helper; no new dep).
 
 ### 8. Public API (`index.ts`) ✅
@@ -148,7 +150,8 @@ consumers share them (see Open decisions).
 
 - `state.ts` — derived render state: enabled surfaces, route matching,
   candidate selection, stacking index/stackSize.
-- `stacking.ts` — positioning process: step length, alignment, limit.
+- `stacking.ts` — positioning process: step length, alignment, limit, z ramp,
+  tilt.
 - `setup.ts` — seeding + bare-type expansion.
 - `mount.ts` — mount tree resolution (table/hud/child, children refs).
 - `partView.tsx` — geometry from a part def (size/fillet/crop), sprite UVs.