fix: clean Yarn 4.x PnP files before yarn install

PnP files (.pnp.cjs, .pnp.d.ts, .pnp.loader.mjs) can cause stale
typescript patch resolution errors (ENOENT _tsc.js). Clean them
before yarn install and before retry.

npm_install_multiversion.py

@@ -2034,6 +2034,12 @@ def _build_frontend(src_frontend: Path, dest_frontend: Path):
         except Exception:
             pass
 
+        # Clean Yarn 4.x PnP files that can cause stale patch resolution
+        for pnp_file in [".pnp.cjs", ".pnp.d.ts", ".pnp.loader.mjs"]:
+            p = src_frontend / pnp_file
+            if p.exists():
+                p.unlink()
+
         # Clean cache
         try:
             run(yarn_cmd + ["cache", "clean"], check=False)