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>

.dockerignore

@@ -0,0 +1,15 @@
+node_modules
+.next
+.git
+.gitignore
+data
+*.tsbuildinfo
+next-env.d.ts
+.env*
+README.md
+Dockerfile
+.dockerignore
+docker-compose.yml
+npm-debug.log*
+.pnpm-debug.log*
+.DS_Store