chore: upgrade to next 16 + react 19

- next 14.2 -> 16.2, react/react-dom 18 -> 19, eslint 8 -> 9,
  typescript-eslint 6 -> 8, typescript 5.3 -> 5.7, @types/react* -> 19
- remove i18n config from next.config.js (unsupported in App Router; it
  forced a pages-router _document and broke the 404 prerender)
- Next 16 reconfigured tsconfig (moduleResolution bundler, jsx react-jsx)

Build, unit tests, and e2e all green on the new stack.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web/next-env.d.ts

@@ -1,5 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
+import "./.next/dev/types/routes.d.ts";
 
 // NOTE: This file should not be edited
-// see https://nextjs.org/docs/app/building-your-application/configuring/typescript for more information.
+// see https://nextjs.org/docs/app/api-reference/config/typescript for more information.

web/next.config.js

@@ -1,10 +1,6 @@
 /** @type {import('next').NextConfig} */
 const nextConfig = {
   reactStrictMode: true,
-  i18n: {
-    locales: ['en-US'],
-    defaultLocale: 'en-US',
-  },
   output: 'standalone',
 
   async redirects() {

web/package.json

@@ -44,14 +44,14 @@
     "cmdk": "^1.1.1",
     "date-fns": "^4.1.0",
     "lucide-react": "^0.453.0",
-    "next": "14.2.26",
+    "next": "16.2.10",
     "next-auth": "^4.24.10",
     "next-themes": "^0.4.3",
     "papaparse": "^5.4.1",
     "prisma": "^5.22.0",
-    "react": "^18.2.0",
+    "react": "^19.2.0",
     "react-day-picker": "^9.9.0",
-    "react-dom": "^18.2.0",
+    "react-dom": "^19.2.0",
     "react-dropzone": "^14.3.5",
     "react-hook-form": "^7.53.1",
     "react-qr-code": "^2.0.12",
@@ -75,16 +75,16 @@
     "jsdom": "^25.0.1",
     "msw": "^2.7.0",
     "vitest": "^2.1.8",
-    "@types/node": "20.11.5",
-    "@types/react": "18.2.48",
-    "@types/react-dom": "18.2.18",
-    "@typescript-eslint/eslint-plugin": "^6.19.0",
-    "@typescript-eslint/parser": "^6.19.0",
+    "@types/node": "^20.11.5",
+    "@types/react": "^19.2.0",
+    "@types/react-dom": "^19.2.0",
+    "@typescript-eslint/eslint-plugin": "^8.18.0",
+    "@typescript-eslint/parser": "^8.18.0",
     "autoprefixer": "^10.4.20",
-    "eslint": "8.56.0",
-    "eslint-config-next": "14.1.0",
+    "eslint": "^9.17.0",
+    "eslint-config-next": "16.2.10",
     "postcss": "^8.4.47",
     "tailwindcss": "^3.4.14",
-    "typescript": "5.3.3"
+    "typescript": "^5.7.2"
   }
 }

web/tsconfig.json

@@ -1,10 +1,16 @@
 {
   "compilerOptions": {
     "target": "es5",
-    "lib": ["dom", "dom.iterable", "esnext"],
+    "lib": [
+      "dom",
+      "dom.iterable",
+      "esnext"
+    ],
     "baseUrl": ".",
     "paths": {
-      "@/*": ["./*"]
+      "@/*": [
+        "./*"
+      ]
     },
     "allowJs": true,
     "skipLibCheck": true,
@@ -13,18 +19,26 @@
     "noEmit": true,
     "esModuleInterop": true,
     "module": "esnext",
-    "moduleResolution": "node",
+    "moduleResolution": "bundler",
     "resolveJsonModule": true,
     "isolatedModules": true,
-    "jsx": "preserve",
+    "jsx": "react-jsx",
     "incremental": true,
     "plugins": [
       {
         "name": "next"
       }
     ],
-    "strictNullChecks": false,
+    "strictNullChecks": false
   },
-  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
-  "exclude": ["node_modules"]
+  "include": [
+    "next-env.d.ts",
+    "**/*.ts",
+    "**/*.tsx",
+    ".next/types/**/*.ts",
+    ".next/dev/types/**/*.ts"
+  ],
+  "exclude": [
+    "node_modules"
+  ]
 }