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>

package.json

@@ -0,0 +1,28 @@
+{
+  "name": "retroblog",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "dev": "next dev",
+    "build": "next build",
+    "start": "next start",
+    "lint": "eslint"
+  },
+  "dependencies": {
+    "better-sqlite3": "^12.10.0",
+    "marked": "^18.0.5",
+    "next": "16.2.7",
+    "react": "19.2.4",
+    "react-dom": "19.2.4",
+    "server-only": "^0.0.1"
+  },
+  "devDependencies": {
+    "@types/better-sqlite3": "^7.6.13",
+    "@types/node": "^20",
+    "@types/react": "^19",
+    "@types/react-dom": "^19",
+    "eslint": "^9",
+    "eslint-config-next": "16.2.7",
+    "typescript": "^5"
+  }
+}