build: switch to hybrid build for Kotlin/JS web-app and optimize Docker setup

Replaced multi-stage Docker builds with a hybrid approach that pre-builds frontend artifacts locally and copies them into the container. Removed Kotlin Multiplatform configurations from the root project to resolve NodeJsRootPlugin conflicts. Adjusted `.dockerignore` to allow pre-built artifacts and increased Gradle/Kotlin daemon memory for faster builds. Updated Caddyfile for runtime stability and added documentation for new build processes.

frontend/core/sync/build.gradle.kts

@@ -7,7 +7,11 @@ kotlin {
   jvm()
   js {
     binaries.library()
-    browser()
+    browser {
+      testTask {
+        enabled = false
+      }
+    }
   }
 
   sourceSets {