initial: Kotlin/Gradle skeleton for cloud-installer

Compiles to a 3.4 MB fat jar via shadow plugin.
Entrypoint with CLI dispatch (pull/push subcommands) + FlatLaf init.
Real sync logic stubbed; lands in subsequent commits per task plan.

Build via containerized gradle (8.10.2 + jdk21) to sidestep the
Kotlin 2.1 + JDK 26 compiler crash. Documented in README.

CI workflow tags-only release artifact upload prepared (needs
RELEASE_TOKEN secret in repo settings before first tag).

build.gradle.kts

@@ -0,0 +1,61 @@
+plugins {
+    kotlin("jvm") version "2.1.0"
+    kotlin("plugin.serialization") version "2.1.0"
+    id("com.gradleup.shadow") version "8.3.5"
+    application
+}
+
+group = "center.timemachine.cloud"
+version = "0.1.0"
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    // FlatLaf gives us an IntelliJ-style dark theme on Swing —
+    // closest visual match to Prism Launcher's Qt look in pure Java.
+    implementation("com.formdev:flatlaf:3.5.4")
+    implementation("com.formdev:flatlaf-intellij-themes:3.5.4")
+
+    // JSON via Kotlin's official lib; supports kotlin data classes natively.
+    implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.7.3")
+
+    testImplementation(kotlin("test"))
+    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.10.2")
+}
+
+// Target Java 17 bytecode using whatever JDK is installed locally (we
+// require >= 17). Avoids the Gradle toolchain auto-provisioning dance,
+// at the cost of needing a manual JDK 17+ on dev machines and CI runners.
+kotlin {
+    compilerOptions {
+        jvmTarget.set(org.jetbrains.kotlin.gradle.dsl.JvmTarget.JVM_17)
+    }
+}
+
+java {
+    sourceCompatibility = JavaVersion.VERSION_17
+    targetCompatibility = JavaVersion.VERSION_17
+}
+
+application {
+    mainClass.set("center.timemachine.cloud.MainKt")
+}
+
+tasks.test {
+    useJUnitPlatform()
+}
+
+tasks.shadowJar {
+    archiveBaseName.set("cloud-installer")
+    archiveClassifier.set("")
+    archiveVersion.set(project.version.toString())
+    mergeServiceFiles()
+}
+
+// Defer to shadowJar for the canonical artifact; the default 'jar' task
+// produces a thin jar without dependencies which would be useless to ship.
+tasks.jar {
+    enabled = false
+}