feat(mesh): render cards, tiles, and tokens with separated front/back/walls

Split extrudeShapeParts into front, back, and walls so each face can carry
its own material. Flip back textures left/right on the material so they are
not mirrored, and slice card faces from the deck sprite sheet via CardID.
Resolve deck config from the parent deck, which is authoritative over a
card's own CustomDeck. Add unit tests for card resolution, sprite UVs, and
the flip helper.

apps/web/src/components/viewers/register.ts

@@ -14,6 +14,7 @@ registerViewer('Tile', TileViewer);
 registerViewer('Custom_Tile', TileViewer);
 registerViewer('Custom_Token', TokenViewer);
 registerViewer('Card', CardViewer);
+registerViewer('CardCustom', CardViewer);
 registerViewer('Deck', CardViewer);
 registerViewer('DeckCustom', CardViewer);
 registerViewer('Custom_Deck', CardViewer);