feat: extract pdf from mp/pdf — initial libreshop/pdf

Source moved verbatim from mp/pdf/ on 2026-04-29; mp was the first
concrete adapter consuming the libreshop toolkit. Builds and publishes
git.librete.ch/libreshop/pdf on every main / v* push via the standard
.gitea/workflows/build.yml shared across libreshop components.

makefile

@@ -0,0 +1,15 @@
+TEX = pandoc
+FLAGS = --pdf-engine=xelatex
+
+# Use the values of src, template, and output passed as arguments
+$(output) : $(src)
+	$(TEX) $(src) -o $@ --template=$(template) $(FLAGS)
+
+.PHONY: clean
+clean :
+	rm -f /app/data/output/*.pdf
+
+.PHONY: cleanall
+cleanall : clean
+	rm -rf /app/data/output/*
+