Rewrite songbook as pure LaTeX project (Carmina Leonis style)

Replace the Kotlin/Gradle multi-module pipeline with a pure LaTeX
songbook using the leadsheets package and LuaLaTeX. Style matches
the Carmina Leonis (CL6) scout songbook: Fraktur titles, chords
above lyrics, metadata at page bottom, reference book footer.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

songs/hejo-spann-den-wagen-an.tex

@@ -0,0 +1,24 @@
+\begin{song}{
+  title = {Hejo, spann den Wagen an},
+  lyrics = Traditionell,
+  composer = Traditionell,
+  key = Am,
+  tags = {Kanon, Fahrt},
+  mundorgel = 15,
+}
+
+\begin{verse*}
+Kanon: \\
+\chord{Am}Hejo, spann den Wagen an, \\
+denn der \chord{G}Wind treibt \chord{Am}Regen übers Land. \\
+\chord{Am}Hol die goldnen Garben rein, \\
+denn der \chord{G}Wind treibt \chord{Am}Regen übers Land.
+\end{verse*}
+
+\begin{verse*}
+2. Stimme: \\
+\chord{Am}Hejo, spann den Wagen an, \\
+denn der \chord{G}Wind treibt \chord{Am}Regen übers Land.
+\end{verse*}
+
+\end{song}