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/bus/emt-madrid.org

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+:PROPERTIES:
+:ID:       emt-madrid
+:END:
+#+title: EMT Madrid (urban bus)
+
+Empresa Municipal de Transportes (EMT) operates the urban bus network
+within the municipality of Madrid — around 200 lines.
+
+* Notable lines
+- *Line 27* — connects Embajadores with Barrio de la Concepción, one of the
+  oldest routes in the network.
+- *Line 34* — Argüelles to Carabanchel, crossing the city centre via Gran Vía.
+- *Búho (owl) lines* — night buses running from Cibeles from midnight to 6 am.
+
+* See also
+- [[id:madrid-transport][Madrid Public Transport]]

notes/madrid-transport.org

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+:PROPERTIES:
+:ID:       madrid-transport
+:END:
+#+title: Madrid Public Transport
+
+Madrid has one of the most extensive public transport networks in Europe,
+operated primarily by [[id:crtm][Consorcio Regional de Transportes de Madrid]] (CRTM).
+
+* Modes
+- [[id:metro-madrid][Metro de Madrid]] — 13 lines, ~300 km of track
+- [[id:emt-madrid][EMT Bus]] — urban buses within the city
+- Cercanías — suburban rail run by Renfe
+- Interurbano — regional buses to the wider Community of Madrid
+
+* Ticketing
+A single [[https://www.crtm.es][tarjeta transporte]] (transport card) works across all modes.
+The Multi card covers zones A–C and is topped up at any metro station.

notes/metro/metro-madrid.org

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+:PROPERTIES:
+:ID:       metro-madrid
+:END:
+#+title: Metro de Madrid
+
+The Madrid Metro is the main rapid transit network in the city, opened in 1919.
+It is the second oldest metro in the Iberian Peninsula after Barcelona.
+
+* Key Lines
+| Line | Name            | Colour | Terminals                    |
+|------+-----------------+--------+------------------------------|
+| L1   | Pinar de Chamartín–Valdecarros | Blue   | Pinar de Chamartín / Valdecarros |
+| L6   | Circular        | Grey   | Circular (loop)              |
+| L10  | —               | Dark blue | Hospital Infanta Sofía / Tres Olivos |
+
+* See also
+- [[id:madrid-transport][Madrid Public Transport]]
+- [[id:sol-interchange][Sol interchange]]

notes/metro/sol-interchange.org

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+:PROPERTIES:
+:ID:       sol-interchange
+:END:
+#+title: Sol (interchange)
+
+Sol is the busiest interchange station in the Madrid Metro, sitting beneath
+Puerta del Sol in the city centre.
+
+Lines serving Sol: [[id:metro-madrid][L1]], L2, L3.
+
+It also connects to the Cercanías hub underneath, making it the de-facto
+zero point of Madrid's public transport.

notes/roads/crtm.org

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+: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]]

notes/roads/m30.org

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+:PROPERTIES:
+:ID:       m30
+:END:
+#+title: M-30
+
+The M-30 is Madrid's innermost ring road, circling the city centre at a
+radius of roughly 3–5 km from Puerta del Sol.
+
+It runs mostly underground through the Madrid Río tunnel section along the
+Manzanares river, built during the 2004–2007 renovation that reclaimed the
+riverbank as a public park.
+
+* Key junctions
+- Nudo Norte — connects to A-1 (Burgos) and A-6 (La Coruña)
+- Nudo Sur — connects to A-4 (Cádiz) and A-42 (Toledo)
+
+* See also
+- [[id:crtm][CRTM]]
+- [[id:madrid-transport][Madrid Public Transport]]