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

notes/roads/crtm.org

@@ -0,0 +1,22 @@
+:PROPERTIES:
+:ID:       crtm
+:END:
+#+title: CRTM — Consorcio Regional de Transportes de Madrid
+
+The CRTM is the regional authority that coordinates public transport across
+the Community of Madrid. It does not operate services directly but sets
+fares, zones, and integration policy.
+
+* Fare zones
+| Zone  | Coverage                    |
+|-------+-----------------------------|
+| A     | Municipality of Madrid      |
+| B1    | Inner ring municipalities   |
+| B2    | Outer ring municipalities   |
+| B3    | Further suburban area       |
+| C1–C2 | Commuter belt               |
+
+* Related
+- [[id:madrid-transport][Madrid Public Transport]]
+- [[id:metro-madrid][Metro de Madrid]]
+- [[id:emt-madrid][EMT Madrid]]