test: add shared shutdown registry helper

Author: heodongun

src/test/kotlin/com/cotor/testsupport/ServiceLifecycleExtensions.kt

@@ -0,0 +1,16 @@
+package com.cotor.testsupport
+
+import com.cotor.app.DesktopAppService
+
+/**
+ * Guarantees DesktopAppService background jobs are stopped even when a test fails.
+ */
+suspend fun <T> withDesktopServiceShutdown(
+    service: DesktopAppService,
+    block: suspend () -> T
+): T =
+    try {
+        block()
+    } finally {
+        service.shutdown()
+    }