feat(tabletop): add state, setup, mounting, and stacking

Implement the tabletop library's game state store, setup seeding with
bare-type expansion, surface mount tree resolution, part placement, and
the stacking positioning process with a dependency-free SVG path helper.
Wire the public API and add unit plus vite integration tests.

packages/tabletop/src/index.ts

@@ -9,4 +9,31 @@ export {
   traceToShape,
   traceToUvBounds,
 } from './part.js';
-export { resolveAssetUrl, assetUrl, traceImage } from './http.js';
+export { resolveAssetUrl, assetUrl, traceImage } from './http.js';
+
+// State store + derived render state.
+export {
+  useTabletopStore,
+  useRenderState,
+  matchRoute,
+  computeRenderState,
+  computeSurfacePlacements,
+  placementKey,
+} from './state.js';
+export type { GameState, Placement } from './state.js';
+
+// Setup seeding.
+export { SetupLoader, seedFromSetup, expandSetupValue } from './setup.js';
+
+// Surface mounting.
+export { resolveMountTree } from './mount.js';
+export type { MountNode, MountTree } from './mount.js';
+export { WorldSurfaceView, SurfaceNode } from './surfaces/WorldSurfaceView.js';
+export { HudSurfaceView } from './surfaces/HudSurfaceView.js';
+
+// Part placement.
+export { PartPlacement } from './placement.js';
+
+// Stacking.
+export { useStacking, stackingOffset, parsePath, pointAt, NO_OFFSET } from './stacking.js';
+export type { StackOffset } from './stacking.js';