fix: move y-prosemirror to dependencies in server-util

server-util unconditionally imports @blocknote/core/yjs which has a hard
runtime import of y-prosemirror. Having it in devDependencies meant it
was stripped from the published tarball, causing ERR_MODULE_NOT_FOUND
for consumers (e.g. the Next.js test app).

Author: nperez0111

packages/server-util/package.json

@@ -60,11 +60,11 @@
     "@blocknote/react": "workspace:^",
     "@tiptap/pm": "^3.13.0",
     "jsdom": "^25.0.1",
+    "y-prosemirror": "^1.3.7",
     "yjs": "^13.6.27"
   },
   "devDependencies": {
     "@types/jsdom": "^21.1.7",
-    "y-prosemirror": "^1.3.7",
     "y-protocols": "^1.0.6",
     "@types/react": "^19.2.3",
     "@types/react-dom": "^19.2.3",