Replace TS game shell with Bevy/Rust client, add auth service, purge legacy archive

- Replace apps/game (TypeScript/Vite/R3F) with a Bevy 0.16 Rust client
  featuring main menu, star map, and flight states
- Add services/auth: Express + better-auth server with SpacetimeDB
  token exchange endpoint
- Delete archive/legacy-static/ (old JS demos, CSS, assets)
- Update docs pages (architecture, gameplay, roadmap, social, overview)
  to reflect Bevy pivot
- Clean up workspace config: remove apps/game from pnpm workspace,
  update dev scripts, tsconfig, and AGENTS.md files
- Add .vscode/settings.json for Rust tooling

package.json

@@ -7,7 +7,7 @@
     "dev": "bash scripts/dev.sh",
     "dev:docs": "pnpm --filter @void-nav/docs dev --port 5173",
     "dev:site": "pnpm --filter @void-nav/site dev --port 5174",
-    "dev:game": "pnpm --filter @void-nav/game dev --port 5175",
+    "dev:game": "echo 'Game app not yet created. Run pnpm create-vite apps/game to scaffold.'",
     "build": "pnpm -r --if-present build",
     "check": "pnpm -r --if-present check",
     "generate:bindings": "spacetime generate"