feat: initialize Gradle multi-module backend and Vite frontend

backend/settings.gradle.kts

@@ -0,0 +1,16 @@
+rootProject.name = "im-system-backend"
+
+pluginManagement {
+    repositories {
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
+
+dependencyResolutionManagement {
+    repositories {
+        mavenCentral()
+    }
+}
+
+include("gateway", "im-service", "log-service")