Initial implementation of songbook toolset

Kotlin/JVM multi-module project for generating a scout songbook PDF
from ChordPro-format text files. Includes ChordPro parser, layout engine
with greedy spread packing for double-page songs, OpenPDF renderer,
CLI (Clikt), Compose Desktop GUI, and 5 sample songs.

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

model/build.gradle.kts

@@ -0,0 +1,3 @@
+plugins {
+    id("songbook-conventions")
+}