feat(tabletop): let candidates inherit and override route stacking

Candidates now carry their own stacking strategy, inheriting the route's
when absent, so the default tilt applies consistently. Drop the now
redundant explicit tilt from the poker deck.

packages/bgm/src/types.ts

@@ -84,6 +84,8 @@ export interface Candidate {
   x?: number;
   y?: number;
   rotation?: number;
+  /** Stacking strategy; overrides the route's when set, else inherits it. */
+  stacking?: Stacking;
 }
 
 export interface Route {