Introduce Vitest for getFailingLine and wire into Gradle build

Extract getFailingLine to a testable utility, add Vitest via NpmTask
so test failures break the build before the vite build runs.

Author: Sonique

ui2/build.gradle.kts

@@ -1,6 +1,5 @@
+import com.github.gradle.node.npm.task.NpmTask
 import com.github.gradle.node.task.NodeTask
-import org.gradle.kotlin.dsl.named
-import org.gradle.kotlin.dsl.tasks
 
 plugins {
     alias(libs.plugins.nodeGradle)
@@ -12,6 +11,15 @@ node {
 }
 
 tasks {
+    register<NpmTask>("viteTest") {
+        args.set(listOf("run", "test"))
+
+        inputs.file("vitest.config.ts")
+        inputs.file("package-lock.json")
+        inputs.dir("src")
+        dependsOn("npmInstall")
+    }
+
     register<NodeTask>("viteBuild") {
         script.set(project.file("node_modules/.bin/vite"))
         args = listOf("build")
@@ -20,7 +28,7 @@ tasks {
         inputs.file("package-lock.json")
         inputs.dir("src")
         outputs.dir("${layout.buildDirectory.get()}/js")
-        dependsOn("npmInstall")
+        dependsOn("npmInstall", "viteTest")
     }
 
     register<NodeTask>("viteDev") {