Import 294 songs from Carmina Leonis PDF

Add import-songs.py script that extracts songs from the PDF text
and generates .tex files with leadsheets format. Adds song
properties for all reference books (BuLiBu, BuLiBuII, CL, SwA,
Barde, LiBock). Generates all-songs.tex with alphabetical inputs.

Note: Chord alignment is approximate from PDF extraction and
may need manual review for some songs.

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

songs/zogen-einst.tex

@@ -0,0 +1,40 @@
+\begin{song}{
+  title = {Zogen einst},
+  lyrics = {Karl Plenzat},
+  composer = {aus Masuren},
+  bulibu = 312,
+  cl = 420,
+  swa = 304,
+  barde = 393,
+  libock = 444,
+}
+
+\begin{verse}
+/: Z \chord{G}ogen ei \chord{C}nst fünf \chord{G}wilde Schwäne, \\
+Schwän \chord{C}e leuc \chord{a}htend weiß \chord{D7}und schön. \chord{G} :/ \\
+/: \chord{D7}Sing, sing, w \chord{G}as geschah? \\
+Kei \chord{D7}ner ward mehr geseh´ \chord{G}n, ja! :/
+\end{verse}
+
+\begin{verse}
+/: Wuchsen einst fünf junge Birken \\
+grün und frisch am Bachesrand. :/ \\
+/: Sing, sing, was geschah? \\
+Keine in Blüte stand. :/
+\end{verse}
+
+\begin{verse}
+/: Zogen einst fünf junge Burschen \\
+stolz und kühn zum Kampf hinaus. :/ \\
+/: Sing, sing, was geschah? \\
+Keiner kehrt mehr nach Haus. :/
+\end{verse}
+
+\begin{verse}
+/: Wuchsen einst fünf junge Mädchen \\
+schlank und schön am Memelstrand. :/ \\
+/: Sing, sing, was geschah? \\
+Keine den Brautkranz wand. :/
+\end{verse}
+
+\end{song}