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

spacetime.json

@@ -0,0 +1,13 @@
+{
+  "database": "void-nav-dev",
+  "module-path": "./services/spacetimedb",
+  "generate": [
+    {
+      "language": "typescript",
+      "out-dir": "./apps/game/src/module_bindings"
+    }
+  ],
+  "dev": {
+    "run": "pnpm --filter @void-nav/game dev --port 5175"
+  }
+}