SDK-613: upgrade Next.js examples to 15.5.25 and add test coverage

The two Next.js examples were pinned to next@14.2.15, which is what the
Dependabot alert on this repo flags. Move both to next@15.5.25 (latest
fully-patched 15.x); `npm audit` no longer reports any advisory against
Next.js itself in either example.

15.x rather than 16.x: Next 16 requires node ^20.9 || >=22, which would
break the node 18 and node 21 legs of the CI matrix, and it removes
`next lint`, which both examples still use.

Alongside the bump:
- react/react-dom and their types move to 19, matching what Next 15's
  App Router expects; @rollbar/react already declares 19.x support.
- Add `outputFileTracingRoot` to both next configs so Next 15 stops
  inferring the repo root as the workspace root (multiple lockfiles).
- Add `target: ES2017` to the app-router tsconfig, as Next 15 requires
  for top-level await.

Test coverage for the upgrade — both examples now run jest via
`next/jest`, so the suites exercise the real SWC/Next transform:
- pages router: `_app` renders the page with a Rollbar instance in
  context, and a throwing page renders the ErrorBoundary fallback and
  reports through `rollbar.critical` with the configured message, extra
  and callback; the home page renders (covers next/font/local and
  next/image under Next 15).
- app router: the async `RootLayout` server component wraps the document
  in the Rollbar Provider, `next_error_handler/error.tsx` reports the
  error via `useRollbar` and resets, and the `ErrorBoundary` page renders.

Wired up as `npm run test:examples` (skips examples without a `test:ci`
script) and run as a new CI step.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: AI Agent

.github/workflows/ci.yaml

@@ -67,6 +67,9 @@ jobs:
       - name: Test
         run: npm run test
 
+      - name: Test examples
+        run: npm run test:examples
+
   install:
     runs-on: ubuntu-latest
 

examples/nextjs-approuter/jest.config.js

@@ -0,0 +1,12 @@
+const nextJest = require('next/jest');
+
+const createJestConfig = nextJest({ dir: './' });
+
+/** @type {import('jest').Config} */
+const jestConfig = {
+  setupFilesAfterEnv: ['<rootDir>/jest.setup.ts'],
+  testEnvironment: 'jest-environment-jsdom',
+  testMatch: ['<rootDir>/src/__tests__/**/*.test.tsx'],
+};
+
+module.exports = createJestConfig(jestConfig);

examples/nextjs-approuter/jest.setup.ts

@@ -0,0 +1 @@
+import '@testing-library/jest-dom';

examples/nextjs-approuter/next.config.mjs

@@ -1,4 +1,13 @@
+import { fileURLToPath } from 'url';
+import path from 'path';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
 /** @type {import('next').NextConfig} */
-const nextConfig = {};
+const nextConfig = {
+  // This example lives inside the @rollbar/react repo, so Next.js would
+  // otherwise infer the repo root as the workspace root.
+  outputFileTracingRoot: __dirname,
+};
 
 export default nextConfig;