SDK-613: move the Next.js examples to 16.3.4 and drop node 18 from CI

Follow-up to the 15.5.25 bump: go all the way to the current Next.js
major. `npm audit` in both examples now reports nothing against `next`
at all (the transitive `postcss` advisories 15.x carried are gone too).

Next 16 requires node >= 20.9, so the node 18 leg of the CI matrix is
removed; node 22 is added so the matrix still covers three versions.

Next 16 also removes `next lint`, and `eslint-config-next@16` is
flat-config only and needs ESLint >= 9. So both examples:
- replace `.eslintrc.json` with `eslint.config.mjs` re-exporting
  `eslint-config-next/core-web-vitals` (which already carries the
  TypeScript setup and the .next/out/build ignores),
- move eslint 8 -> 9, and
- change their `lint` script from `next lint` to `eslint .`.

ESLint is pinned to ^9 rather than ^10 deliberately: eslint-config-next
16 pulls eslint-plugin-react, eslint-plugin-import and
eslint-plugin-jsx-a11y, none of which declare ESLint 10 support yet, so
^10 only installs behind three ERESOLVE peer overrides.

The root `lint:examples` script still works unchanged -- ESLint 9 still
accepts `--ext` -- and both examples lint clean via either invocation.

tsconfig `jsx` moves from `preserve` to `react-jsx`, which Next 16
mandates, and the app-router example picks up the `.next/dev/types`
include.

Verified: both examples build (Turbopack), lint clean, and all six
example tests added for this upgrade still pass.

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

Author: AI Agent

.github/workflows/ci.yaml

@@ -15,12 +15,13 @@ jobs:
     strategy:
       matrix:
         include:
-          - node: 18
-            npm: 9
+          # Next.js 16 (used by the examples) requires node >= 20.9.
           - node: 20
             npm: 10
           - node: 21
             npm: 10
+          - node: 22
+            npm: 10
 
     continue-on-error: true
 

examples/nextjs-approuter/.eslintrc.json

@@ -0,0 +1,9 @@
+import nextCoreWebVitals from 'eslint-config-next/core-web-vitals';
+
+// Next 16 removed `next lint`, so ESLint runs directly against this flat
+// config. `eslint-config-next/core-web-vitals` already brings the TypeScript
+// setup and the `.next`/`out`/`build` ignores with it.
+/** @type {import('eslint').Linter.Config[]} */
+const config = [...nextCoreWebVitals];
+
+export default config;