fix: Add build jar configuration (#86)

Add jar config to build aplication with correct Main-Class into MANIFEST.MF

samples/kotlin-mcp-server/build.gradle.kts

@@ -23,3 +23,13 @@ tasks.test {
 kotlin {
     jvmToolchain(21)
 }
+
+tasks.jar {
+    manifest {
+        attributes["Main-Class"] = "MainKt"
+    }
+
+    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
+
+    from(configurations.runtimeClasspath.get().map { if (it.isDirectory) it else zipTree(it) })
+}