Enable Maven Central publishing for audioplayer

The module configured coordinates and POM but never called
publishToMavenCentral(), so the vanniktech plugin did not create the
publishAndReleaseToMavenCentral task and the release workflow silently
published only :mediaplayer. Also sign publications in CI like mediaplayer.

Author: kdroidFilter

audioplayer/build.gradle.kts

@@ -135,4 +135,11 @@ mavenPublishing {
             url.set("https://github.com/kdroidFilter/Compose-Media-Player")
         }
     }
+
+    publishToMavenCentral()
+
+    // Only sign publications in CI environments to avoid requiring local GPG signing setup.
+    if (System.getenv("CI") != null) {
+        signAllPublications()
+    }
 }