Migrate blog from Gatsby to Next.js (App Router) and update deploy workflow

[suu3]

Motivation

• Replace the existing Gatsby site with a Next.js App Router-based static site to simplify structure and use Next.js static export.
• Update CI/CD to modern tool versions and ensure the static out/ folder is deployed to GitHub Pages.

Description

• Removed Gatsby-specific configuration, plugins, templates, and many legacy React components and styles, and added a Next.js app/ structure with app/layout.tsx, app/page.tsx, category and post routes, global CSS, and UI components like PostSearch.
• Added lib/posts.ts for markdown content ingestion, next.config.ts with output: 'export', moved static assets into public/, and created public/site.webmanifest for PWA metadata.
• Reworked project metadata and dependencies in package.json to remove Gatsby dependencies and add next, react/react-dom v19, gray-matter, TypeScript and Tailwind-related dev deps, and updated npm scripts to dev, build, start, and lint.
• Updated tooling and CI: tsconfig.json adjusted for Next, postcss.config.ts switched to Tailwind plugin, .gitignore updated, and GitHub Actions deploy.yml bumped actions versions, switched Node to 20, pnpm to v9, installs with --frozen-lockfile, builds with pnpm run build, and deploys ./out via peaceiris/actions-gh-pages@v4.

Testing

• No automated tests were executed as part of this change; CI workflow was updated but not run in this PR.

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Codex Task

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Regenerate lockfile before frozen install in CI

The workflow now runs pnpm install --frozen-lockfile, but this commit also replaces the dependency set in package.json without updating pnpm-lock.yaml; pnpm documents that frozen mode "fail[s] if an update is needed," and at this revision install fails with ERR_PNPM_OUTDATED_LOCKFILE. That means every deploy job will stop at dependency installation and no static build/deploy can complete until the lockfile is regenerated and committed.

Useful? React with 👍 / 👎.

[chatgpt-codex-connector]

Render markdown content instead of raw source text

The post page prints post.content inside a <pre>, so markdown is displayed as literal source (e.g., headings, links, code fences, image syntax) rather than rendered article content. For this blog’s markdown-based posts, readers lose formatted content and media rendering on every post detail page, which is a major functional regression from the previous behavior.

Useful? React with 👍 / 👎.