Use JavaFX Gradle plugin for proper module path setup

Replace manual classifier-based jar deps with the openjfx javafx-plugin
which correctly sets up the JavaFX module path, native lib paths, and
JVM args needed for media codecs (AVFoundation on macOS).

This fixes 'media type not supported' which was caused by JavaFX being
on classpath instead of module path — native .dylib codecs only load
when JavaFX runs as a named module.

gradle/libs.versions.toml

@@ -5,6 +5,7 @@ coroutines = "1.8.0"
 serialization = "1.6.3"
 slf4j = "2.0.12"
 logback = "1.5.3"
+javafx = "21.0.3"
 
 [libraries]
 kotlin-stdlib = { module = "org.jetbrains.kotlin:kotlin-stdlib", version.ref = "kotlin" }
@@ -18,3 +19,4 @@ logback-classic = { module = "ch.qos.logback:logback-classic", version.ref = "lo
 kotlin-jvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
 kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }
 compose-multiplatform = { id = "org.jetbrains.compose", version.ref = "compose" }
+javafx = { id = "org.openjfx.javafxplugin", version = "0.1.0" }