Restructure into pnpm monorepo with game shell, docs, and SpacetimeDB backend

- Restructure flat static prototype into pnpm workspace monorepo
- apps/game: playable shell with R3F 3D scene, HUD, SpacetimeDB connection
- apps/docs: design docs and prototypes
- apps/site: landing page
- packages/ui: shared Button and Panel primitives
- services/spacetimedb: backend module (9 tables, 11 reducers)
- Archive legacy static files to archive/legacy-static/
- Game loop: connect, undock, target, approach, dock, mine, sell
- Add pnpm-workspace.yaml, tsconfig.base.json, spacetime.json

archive/legacy-static/js/router.js

@@ -0,0 +1,25 @@
+window.GDD = window.GDD || {};
+
+const { useState, useEffect, useCallback } = React;
+
+/* Hash-based router */
+window.GDD.useRouter = function() {
+  const [page, setPage] = useState(getPage());
+
+  function getPage() {
+    const hash = window.location.hash.slice(1) || 'overview';
+    return hash;
+  }
+
+  useEffect(() => {
+    const handler = () => setPage(getPage());
+    window.addEventListener('hashchange', handler);
+    return () => window.removeEventListener('hashchange', handler);
+  }, []);
+
+  const navigate = useCallback((path) => {
+    window.location.hash = path;
+  }, []);
+
+  return { page, navigate };
+};