build(docker): consolidate WASM build into multi-stage Dockerfile

- Move WASM compilation from GitHub Actions into Docker build stages
- Add emsdkVersion to package.json config as single source of truth
- Implement cargo-chef for dependency caching in both WASM and server builds
- Update .dockerignore to include packed game assets while excluding unpacked
- Simplify deploy workflow by removing local WASM build steps

package.json

@@ -2,6 +2,9 @@
   "name": "pacman",
   "type": "module",
   "packageManager": "bun@^1.3.5",
+  "config": {
+    "emsdkVersion": "4.0.22"
+  },
   "engines": {
     "bun": ">=1.3.5"
   },