fix(deps): update nextjs monorepo to v15 (major) (#45)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

package.json

@@ -12,7 +12,7 @@
   },
   "dependencies": {
     "@react-email/components": "0.1.1",
-    "next": "14.2.30",
+    "next": "15.3.5",
     "react": "19.1.0",
     "react-dom": "19.1.0",
     "resend": "latest"
@@ -22,7 +22,7 @@
     "@types/react": "19.1.8",
     "@types/react-dom": "19.1.6",
     "eslint": "8.56.0",
-    "eslint-config-next": "14.1.0",
+    "eslint-config-next": "15.3.5",
     "prettier": "3.2.5",
     "typescript": "5.8.3"
   }