fix: downgrade Next.js to v15 for Cloudflare Workers compatibility

  Next.js 16 causes runtime error on Cloudflare Workers: "Cannot assign to read only property 'setImmediate'"

  - Downgrade next from 16.1.1 to 15.5.9
  - Update tsconfig.json jsx setting (auto-changed by Next.js)
  - Add .open-next and next-env.d.ts to ESLint ignores

Author: fbsobreira

eslint.config.mjs

@@ -8,7 +8,7 @@ import globals from "globals";
 export default [
   js.configs.recommended,
   {
-    ignores: [".next/**", "node_modules/**", "out/**"],
+    ignores: [".next/**", ".open-next/**", "node_modules/**", "out/**", "next-env.d.ts"],
   },
   {
     files: ["**/*.{ts,tsx}"],

package.json

@@ -19,7 +19,7 @@
     "d3-sankey": "^0.12.3",
     "d3-shape": "^3.2.0",
     "framer-motion": "^12.25.0",
-    "next": "^16.1.1",
+    "next": "^15.5.9",
     "react": "^19.2.3",
     "react-dom": "^19.2.3",
     "viem": "^2.44.1",
@@ -39,7 +39,7 @@
     "@typescript-eslint/eslint-plugin": "^8.52.0",
     "@typescript-eslint/parser": "^8.52.0",
     "eslint": "^9.39.2",
-    "eslint-config-next": "^16.1.1",
+    "eslint-config-next": "^15.5.9",
     "eslint-plugin-react": "^7.37.5",
     "eslint-plugin-react-hooks": "^7.0.1",
     "globals": "^17.0.0",