fix(ci): copy Libertinus OTFs into fontconfig's scan path

The preflight check from the previous commit caught it before the
PDF build started:

  MISSING font: Libertinus Serif
  MISSING font: Libertinus Sans
  ERROR: required font not visible to fontconfig.

Root cause: texlive-fonts-extra installs LibertinusSerif-Regular.otf
and siblings into /usr/share/texlive/texmf-dist/fonts/opentype/
public/libertinus-fonts/, but on ubuntu-latest the texlive package
does NOT install a fontconfig snippet that exposes TeX Live's font
tree to fc-list. So `fc-cache -f` alone won't make Libertinus
visible by family name even though the files are on disk.

Fix: after apt-installing texlive-fonts-extra, locate the Libertinus
OTF files via kpsewhich (version-agnostic) and copy them into
/usr/local/share/fonts/libertinus/, which fontconfig always scans.
Then `fc-cache -f` makes fontspec resolve 'Libertinus Serif' /
'Libertinus Sans' / 'Libertinus Mono' / 'Libertinus Math' by family
name.

The preflight verification from the previous commit stays — it now
serves as a post-condition check that the copy actually worked.

Author: leogalambos

.github/workflows/release.yml

@@ -84,11 +84,23 @@ jobs:
             texlive-pictures \
             lmodern \
             fonts-dejavu
-          # texlive-fonts-extra ships Libertinus Serif / Sans under
-          # /usr/share/texlive/texmf-dist/fonts/opentype/public/libertinus-fonts/.
-          # On Ubuntu the texlive package installs a fontconfig snippet that
-          # exposes this path; refresh the fontconfig cache so xelatex's
-          # fontspec can locate Libertinus by family name.
+          # texlive-fonts-extra ships Libertinus Serif / Sans / Mono OTF
+          # files inside TeX Live's font tree, but Ubuntu's texlive package
+          # does NOT register that tree with fontconfig — so xelatex's
+          # fontspec can't find them by family name. Copy the OTFs into
+          # /usr/local/share/fonts/ (a path fontconfig always scans) and
+          # refresh the cache so 'Libertinus Serif' resolves at PDF build
+          # time. kpsewhich locates the file regardless of TeX Live
+          # version-specific path layout.
+          LIBERTINUS_OTF=$(kpsewhich -format=opentype\ fonts LibertinusSerif-Regular.otf || true)
+          if [ -n "$LIBERTINUS_OTF" ] && [ -f "$LIBERTINUS_OTF" ]; then
+            LIBERTINUS_DIR=$(dirname "$LIBERTINUS_OTF")
+            sudo mkdir -p /usr/local/share/fonts/libertinus
+            sudo cp "$LIBERTINUS_DIR"/*.otf /usr/local/share/fonts/libertinus/
+            echo "Copied Libertinus OTF files from $LIBERTINUS_DIR"
+          else
+            echo "WARNING: LibertinusSerif-Regular.otf not found via kpsewhich"
+          fi
           sudo fc-cache -f >/dev/null 2>&1 || true
 
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