fix(deps): update nextjs monorepo to v15.2.1

Author: renovate[bot]

package-lock.json

@@ -36,7 +36,7 @@
     "date-fns": "^3.6.0",
     "dotenv": "^16.3.1",
     "eslint": "8.57.1",
-    "eslint-config-next": "15.1.3",
+    "eslint-config-next": "15.2.1",
     "i18next": "24.2.1",
     "i18next-browser-languagedetector": "^8.0.0",
     "i18next-resources-to-backend": "^1.1.4",
@@ -45,7 +45,7 @@
     "mailparser": "^3.7.0",
     "mui-tiptap": "^1.17.0",
     "nanoid": "^5.0.1",
-    "next": "15.1.3",
+    "next": "15.2.1",
     "react": "19.0.0",
     "react-dom": "19.0.0",
     "react-dropzone": "^14.2.3",