chore: upgrade blog example to Next.js 16

[qqpann]

Summary

• upgrade the Next.js blog example to Next.js 16.2.10 and React 19.2.7
• update React types, Tailwind CSS 3, and PostCSS, and declare the previously hoisted clsx and tailwind-merge dependencies
• apply the React 19 and Next.js 16 TypeScript migrations
• handle an empty NotCMS database without crashing and regenerate the corrupted favicon
• build the example in CI against a local mock NotCMS API
• add the required changeset

This supersedes the stale dependency updates in #19 and #23.

Why

The example was pinned to unsupported Next.js 14 and React 18 versions. Its existing CI only built and tested the SDK, so missing direct dependencies, React 19 type incompatibilities, and a corrupted favicon were not detected. The blog list also assumed at least one page existed and crashed when the API returned an empty dataset.

PostCSS remains a direct development dependency because Tailwind CSS 3 runs as a PostCSS plugin through the example's postcss.config.mjs.

Impact

The example now uses the current Next.js 16 and React 19 releases and is verified as a standalone workspace project. The SDK runtime API is unchanged.

The published dependency tarballs and lifecycle scripts were reviewed before installation. [email protected], an optional Next.js dependency, is allowed explicitly for its reviewed install check.

Validation

• pnpm install --frozen-lockfile
• pnpm check
• pnpm --filter notcms build
• pnpm --filter notcms typecheck
• pnpm --filter notcms exec vitest run — 30 passed, 2 skipped
• pnpm --filter blog-demo build:ci
• git diff --check