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>

gui/build.gradle.kts

@@ -0,0 +1,20 @@
+plugins {
+    id("songbook-conventions")
+    id("org.jetbrains.compose")
+    id("org.jetbrains.kotlin.plugin.compose")
+}
+
+dependencies {
+    implementation(project(":app"))
+    implementation(project(":model"))
+    implementation(project(":parser"))
+    implementation(compose.desktop.currentOs)
+    implementation("io.github.microutils:kotlin-logging-jvm:3.0.5")
+    implementation("ch.qos.logback:logback-classic:1.5.16")
+}
+
+compose.desktop {
+    application {
+        mainClass = "de.pfadfinder.songbook.gui.AppKt"
+    }
+}