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

apps/AGENTS.md

@@ -5,7 +5,7 @@ Three Vite + React apps, each independently buildable and dev-serveable.
 | App | Port | Package | Description |
 |-----|------|---------|-------------|
 | `docs` | 5173 | `@void-nav/docs` | Living design docs, 16 doc pages, 14 interactive demos, game-slice prototype |
-| `game` | 5175 | `@void-nav/game` | Playable game client connected to SpacetimeDB backend |
+| `game` | 5175 | `@void-nav/game` | Playable single-player game client connected to SpacetimeDB backend |
 | `site` | 5174 | `@void-nav/site` | Public landing page / marketing site |
 
 ## Shared