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

scripts/dev.sh

@@ -45,14 +45,14 @@ PIDS+=($!)
 
 sleep 3
 
-echo "[dev] Starting game dev server on http://localhost:5175 ..."
-pnpm --filter @void-nav/game dev --port 5175 &
+echo "[dev] Starting auth server on http://localhost:4000 ..."
+pnpm --filter @void-nav/auth dev &
 PIDS+=($!)
 
 echo ""
 echo "=== VOID::NAV Dev Environment ==="
 echo "  SpacetimeDB:  $STDB_HOST"
-echo "  Game:         http://localhost:5175"
+echo "  Auth:         http://localhost:4000"
 echo "  Data dir:     $STDB_DATA_DIR (ephemeral)"
 echo "  Press Ctrl+C to stop"
 echo "=================================="