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>

eslint.config.mjs

@@ -0,0 +1,18 @@
+import { defineConfig, globalIgnores } from "eslint/config";
+import nextVitals from "eslint-config-next/core-web-vitals";
+import nextTs from "eslint-config-next/typescript";
+
+const eslintConfig = defineConfig([
+  ...nextVitals,
+  ...nextTs,
+  // Override default ignores of eslint-config-next.
+  globalIgnores([
+    // Default ignores of eslint-config-next:
+    ".next/**",
+    "out/**",
+    "build/**",
+    "next-env.d.ts",
+  ]),
+]);
+
+export default eslintConfig;