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>

.gitignore

@@ -1,22 +1,28 @@
-# Gradle
-.gradle/
-build/
-buildSrc/build/
+# LaTeX build artifacts
+*.aux
+*.log
+*.out
+*.toc
+*.fls
+*.fdb_latexmk
+*.synctex.gz
+*.synctex(busy)
+*.sxd
+*.sxc
 
-# IDE
-.idea/
-*.iml
-.vscode/
+# Output directory
+output/
 
-# OS
+# OS files
 .DS_Store
 Thumbs.db
 
-# Output
-output/
-
-# Kotlin
-*.class
+# Editor files
+.idea/
+*.iml
+.vscode/
+*~
+*.swp
 
 # Claude
 .claude/