Add org-roam workflow: ox-hugo export pipeline and example notes

- Add flake.nix dev shell with Node.js 22, Elixir, and Emacs+ox-hugo
- Add scripts/export.exs: exports org-roam notes to content/ via ox-hugo,
  mirroring subdirectory structure and generating a fallback index.md
- Add npm scripts: export, build:notes, serve:notes
- Configure FrontMatter plugin for TOML (ox-hugo default output)
- Replace ObsidianFlavoredMarkdown with OxHugoFlavouredMarkdown
- Add example notes: Madrid public transport (metro, bus, roads)
- Update README and AGENTS.md with org-roam workflow instructions

README.md

@@ -1,13 +1,71 @@
-# Quartz v4
+# Quartz v4 — org-roam edition
 
-> “[One] who works with the door open gets all kinds of interruptions, but [they] also occasionally gets clues as to what the world is and what might be important.” — Richard Hamming
+> "[One] who works with the door open gets all kinds of interruptions, but [they] also occasionally gets clues as to what the world is and what might be important." — Richard Hamming
 
 Quartz is a set of tools that helps you publish your [digital garden](https://jzhao.xyz/posts/networked-thought) and notes as a website for free.
 
-🔗 Read the documentation and get started: https://quartz.jzhao.xyz/
+This fork adds first-class support for [org-roam](https://www.orgroam.com/) notes via [ox-hugo](https://ox-hugo.scripter.co/).
+
+🔗 Upstream documentation: https://quartz.jzhao.xyz/
 
 [Join the Discord Community](https://discord.gg/cRFFHYye7t)
 
+## Quick Start
+
+### Prerequisites
+
+This project uses Nix. Enter the development shell, which provides Node.js 22, Elixir, and Emacs with ox-hugo:
+
+```bash
+nix develop
+```
+
+All commands below must be run inside this shell.
+
+```bash
+npm install
+```
+
+### Building from org-roam notes
+
+Your org-roam notes live in a separate directory. Point `NOTES_DIR` at it:
+
+```bash
+# Export notes to content/ and build the site
+NOTES_DIR=/path/to/notes npm run build:notes
+
+# Export, build, and serve with hot reload
+NOTES_DIR=/path/to/notes npm run serve:notes
+
+# Export only (wipes content/ and re-exports all .org files)
+NOTES_DIR=/path/to/notes npm run export
+```
+
+The export script mirrors the subdirectory structure of your notes into `content/`
+and generates a fallback `index.md` if your notes don't include one.
+
+### Building without org-roam notes
+
+If you manage `content/` directly with Markdown files:
+
+```bash
+# Build the site
+npx quartz build
+
+# Build and serve with hot reload
+npx quartz build --serve
+```
+
+The site is generated in `public/`. When serving, visit http://localhost:8080.
+
+### Development
+
+```bash
+npm run check    # type check + format check
+npm run format   # auto-format with Prettier
+npm run test     # run tests
+```
+
 ## Sponsors
 
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