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).

src/test/kotlin/center/timemachine/cloud/SmokeTest.kt

@@ -0,0 +1,16 @@
+package center.timemachine.cloud
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class SmokeTest {
+    @Test
+    fun `cli pull returns 0 in skeleton`() {
+        assertEquals(0, Cli.runPull(arrayOf("--url=http://localhost:9091")))
+    }
+
+    @Test
+    fun `cli push returns 0 in skeleton`() {
+        assertEquals(0, Cli.runPush(arrayOf("--url=http://localhost:9091")))
+    }
+}