Bump pixi.js from 8.17.1 to 8.18.1

Bumps [pixi.js](https://github.com/pixijs/pixijs) from 8.17.1 to 8.18.1.
- [Release notes](https://github.com/pixijs/pixijs/releases)
- [Commits](https://github.com/pixijs/pixijs/compare/v8.17.1...v8.18.1)

---
updated-dependencies:
- dependency-name: pixi.js
  dependency-version: 8.18.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

frontend/package.json

@@ -25,7 +25,7 @@
     "@coderline/alphatab": "^1.3.0",
     "@tonejs/midi": "^2.0.6",
     "mitt": "^3.0.1",
-    "pixi.js": "^8.0.0",
+    "pixi.js": "^8.18.1",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
     "smplr": "^0.14.0",