docs: rebrand README + add Docker and bare-metal deploy

- Rewrite README with RetroBlog branding, config table, and two deploy
  paths (Docker Compose + bare-metal/systemd).
- Enable Next.js standalone output for slim runtime images.
- Add multi-stage Dockerfile (builds better-sqlite3 natively, runs as
  non-root, persists /app/data), docker-compose.yml, and .dockerignore.

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

next.config.ts

@@ -1,7 +1,9 @@
 import type { NextConfig } from "next";
 
 const nextConfig: NextConfig = {
-  /* config options here */
+  // Emit a self-contained server in .next/standalone for slim Docker images
+  // and simple bare-metal deploys.
+  output: "standalone",
 };
 
 export default nextConfig;