feat: add Open Graph and social metadata (computorg#72)

Enable `open-graph` and `twitter-card` in Quarto and add a branded
1200x630 social card so links render with an image on social media.
Replace the homepage's HTML `description` (metadata-only on this page)
with a plain sentence so the meta description no longer repeats the
title.

Also improve indexing: set `canonical-url`, drop the trailing slash
from `site-url` for clean absolute URLs, and add a post-render hook to
align sitemap entries with the canonical trailing-slash form.

Fixes computorg#65

Author: jolars

_quarto.yml

@@ -5,10 +5,18 @@ project:
     - "*.qmd"
     - "site/**/*.qmd"
     - "blog/**/*.qmd"
+  post-render:
+    - scripts/fix-sitemap.sh
 website:
   title: COMPUTO
-  site-url: https://computo-journal.org/
+  site-url: https://computo-journal.org
   description: A platform for computational research and reproducibility
+  image: /assets/img/og-image.png
+  image-alt: "Computo, a journal of the French Statistical Society"
+  open-graph:
+    locale: en_US
+  twitter-card:
+    card-style: summary_large_image
   favicon: assets/favicon.ico
   navbar:
     background: primary
@@ -52,6 +60,7 @@ format:
     theme:
       light: [ custom.scss, light.scss ]
       dark: [ custom.scss, dark.scss ]
+    canonical-url: true
     toc: true
     code-copy: true
     code-block-border-left: true

assets/img/og-image.png

@@ -1,7 +1,10 @@
 ---
-description: <h1>COMPUTO</h1> A journal of the <a href="https://sfds.asso.fr/">French
-  Statistical Society <img height="10px" src="assets/img/sfds.png" alt="SFdS"/></a>
-  - ISSN 2824-7795
+description: >-
+  Computo is an open-access journal of the French Statistical Society publishing
+  reproducible computational and algorithmic contributions in statistics and
+  machine learning.
+image: assets/img/og-image.png
+image-alt: "Computo, a journal of the French Statistical Society"
 page-layout: full
 toc: false
 listing:

assets/img/og-image.svg

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Quarto emits sitemap <loc> entries ending in /index.html, while pages'
+# rel="canonical" tags point at the trailing-slash form. Google Search Console
+# then flags the sitemap URLs as duplicates with no chosen canonical.
+# Upstream bug: https://github.com/quarto-dev/quarto-cli/discussions/11398
+
+sitemap="${QUARTO_PROJECT_OUTPUT_DIR:-_site}/sitemap.xml"
+
+[ -f "$sitemap" ] || exit 0
+
+sed -i 's|/index\.html</loc>|/</loc>|g' "$sitemap"