feat: retro blog engine with swappable OS/console themes

Next.js 16 (App Router, TS) + SQLite (better-sqlite3) + marked.

Core: a shared semantic HTML skeleton (rb- classes in Shell.tsx) that
each theme reskins via a scoped [data-theme="..."] CSS file. Theme is
persisted in a cookie, resolved server-side in the root layout, and
swapped live by the client switcher (no reload, no FOUC).

- DB auto-migrates and seeds posts on first run (data/blog.db, gitignored)
- Pages: post list, post detail (markdown), about
- Themes shipped: Windows XP (Luna), Windows 9x, PlayStation 2
- Adding a skin = registry entry + one scoped CSS file

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,44 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/versions
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.pnpm-debug.log*
+
+# env files (can opt-in for committing if needed)
+.env*
+
+# vercel
+.vercel
+
+# typescript
+*.tsbuildinfo
+next-env.d.ts
+
+# blog database
+/data