Extract and insert 97 images from reference PDF into songs

Extract images from the CL6 PDF using pdfimages, map them to songs
via page-to-CL number matching, and insert \songimage commands.
Add insert-images.py script for repeatable extraction.

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

songs/birkenring.tex

@@ -51,4 +51,6 @@ zu dir in den Farben der Welt, dann bleib hier in dem \\
 fröhlichen Birkenring.
 \end{verse}
 
+\songimage{images/img-134.jpg}
+
 \end{song}