fix: use com.synonym groupId for JVM publishing

The JVM groupId was still hardcoded to org.lightningdevkit while Android
correctly used com.synonym. This aligns both by reading group from
gradle.properties, matching the Android pattern.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ovitrif

bindings/kotlin/ldk-node-jvm/build.gradle.kts

@@ -10,4 +10,4 @@ buildscript {
 plugins {
 }
 
-// version is defined in gradle.properties
+// group and version are defined in gradle.properties

bindings/kotlin/ldk-node-jvm/gradle.properties

@@ -1,3 +1,4 @@
 org.gradle.jvmargs=-Xmx1536m
 kotlin.code.style=official
+group=com.synonym
 version=0.7.0-rc.25

bindings/kotlin/ldk-node-jvm/lib/build.gradle.kts

@@ -17,8 +17,7 @@ plugins {
     id("org.jlleitschuh.gradle.ktlint") version "11.6.1"
 }
 
-group = "org.lightningdevkit"
-// version is read from gradle.properties automatically
+// group and version are read from gradle.properties automatically
 
 repositories {
     // Use Maven Central for resolving dependencies.
@@ -89,7 +88,7 @@ afterEvaluate {
     publishing {
         publications {
             create<MavenPublication>("maven") {
-                groupId = "org.lightningdevkit"
+                groupId = providers.gradleProperty("group").orNull ?: "com.synonym"
                 artifactId = "ldk-node-jvm"
                 version = providers.gradleProperty("version").orNull ?: "0.0.0"