chore: enforce pnpm via devEngines

Block accidental npm/yarn install — npm 10.5+ and pnpm 10.x both
honor devEngines.packageManager and refuse to run when it doesn't
match.

Author: B4nan

website/package.json

@@ -48,5 +48,12 @@
         "rimraf": "^6.0.0",
         "typescript": "^6.0.0"
     },
-    "packageManager": "pnpm@10.24.0"
+    "packageManager": "pnpm@10.24.0",
+    "devEngines": {
+        "packageManager": {
+            "name": "pnpm",
+            "version": "10.x",
+            "onFail": "error"
+        }
+    }
 }