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

.gitignore

@@ -1,5 +1,18 @@
 node_modules/
 dist/
+build/
+coverage/
+.turbo/
+.nx/
+.vite/
+.parcel-cache/
+.cache/
+.DS_Store
+.env
+.env.local
+.env.*.local
+spacetime.local.json
 *.tsbuildinfo
 vite.config.js
 vite.config.d.ts
+.playwright-mcp/