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

quartz.config.ts

@@ -55,7 +55,7 @@ const config: QuartzConfig = {
   },
   plugins: {
     transformers: [
-      Plugin.FrontMatter(),
+      Plugin.FrontMatter({ delimiters: "+++", language: "toml" }),
       Plugin.CreatedModifiedDate({
         priority: ["frontmatter", "git", "filesystem"],
       }),
@@ -66,7 +66,11 @@ const config: QuartzConfig = {
         },
         keepBackground: false,
       }),
-      Plugin.ObsidianFlavoredMarkdown({ enableInHtmlEmbed: false }),
+      // OxHugoFlavouredMarkdown must come before GitHubFlavoredMarkdown.
+      // Note: not compatible with ObsidianFlavoredMarkdown — use one or the other.
+      // If ox-hugo exports TOML frontmatter, change FrontMatter to:
+      //   Plugin.FrontMatter({ delims: "+++", language: "toml" })
+      Plugin.OxHugoFlavouredMarkdown(),
       Plugin.GitHubFlavoredMarkdown(),
       Plugin.TableOfContents(),
       Plugin.CrawlLinks({ markdownLinkResolution: "shortest" }),