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/surfaces/WorldSurfaceView.tsx

@@ -0,0 +1,33 @@
+/**
+ * `WorldSurfaceView` — mount a surface in world space.
+ *
+ * Renders a world mount node (a `kind: table` surface and its child surfaces)
+ * at its anchor. Parts on the surface are placed via `PartPlacement` from the
+ * derived render state. A disabled surface isn't part of the mount tree, so
+ * it's never rendered.
+ */
+import type { Package } from '@tts/bgm';
+import { useRenderState } from '../state.js';
+import { PartPlacement } from '../placement.js';
+import type { MountNode } from '../mount.js';
+
+export function WorldSurfaceView({ pkg, node }: { pkg: Package; node: MountNode }) {
+  return <SurfaceNode pkg={pkg} node={node} />;
+}
+
+/** Render a mount node at its anchor, placing parts and recursing into children. */
+export function SurfaceNode({ pkg, node }: { pkg: Package; node: MountNode }) {
+  const placements = useRenderState(pkg);
+  const own = placements.filter((p) => p.surface === node.id);
+
+  return (
+    <group position={[node.x, 0, node.y]} rotation={[0, node.rotation, 0]}>
+      {own.map((p) => (
+        <PartPlacement key={`${p.surface}:${p.piece}`} pkg={pkg} placement={p} />
+      ))}
+      {node.children.map((child) => (
+        <SurfaceNode key={child.id} pkg={pkg} node={child} />
+      ))}
+    </group>
+  );
+}