Update nextjs monorepo to v15.5.6

Author: renovate[bot]

package.json

@@ -34,7 +34,7 @@
     "autoprefixer": "10.4.21",
     "eslint": "9.39.0",
     "marked": "15.0.6",
-    "next": "15.1.3",
+    "next": "15.5.6",
     "postcss": "8.5.6",
     "prisma": "6.1.0",
     "react": "latest",
@@ -59,7 +59,7 @@
     "@storybook/test": "8.4.7",
     "chromatic": "11.29.0",
     "dotenv": "16.4.7",
-    "eslint-config-next": "15.1.3",
+    "eslint-config-next": "15.5.6",
     "eslint-config-prettier": "9.1.2",
     "eslint-plugin-storybook": "0.11.2",
     "husky": "9.1.7",