chore: bump version to 0.4.0, add Gradle 9.6 wrapper, and finalize builds for NSIS, Docker, Fabric, Forge, and Paper

integrations/forge/modern.gradle

@@ -1,5 +1,5 @@
 plugins { id 'net.minecraftforge.gradle' version '7.0.17' }
-def mc = providers.gradleProperty('mcVersion').get()
+def mc = (providers.gradleProperty('mcVersion').orNull ?: project.findProperty('mcVersion') ?: '26.1.2').toString().trim()
 def forgeVersions = ['26.1.2': '64.1.0', '26.2': '65.1.0', '26.3': '66.0.6']
 java.sourceCompatibility = JavaVersion.VERSION_25
 java.targetCompatibility = JavaVersion.VERSION_25