feat: add runtime configuration for Caddy-based SPA containerization

Introduced `config.json` runtime configuration fetch mechanism to support the "Build Once, Deploy Everywhere" pattern. Replaced NGINX with Caddy for SPA deployment, enabling SPA routing, security headers, and static asset management. Updated Gradle and Kotlin/JS build configurations to align with the new runtime environment. Enhanced Dockerfile and health checks for optimized CI/CD workflows and improved SPA delivery.

frontend/core/sync/build.gradle.kts

@@ -4,15 +4,20 @@ plugins {
 }
 
 kotlin {
-  // Targets are configured centrally in the shells/feature modules; here we just provide common code.
   jvm()
   js(IR) {
-    browser()
+    binaries.library()
+    browser {
+        testTask { enabled = false }
+    }
   }
 
   sourceSets {
     commonMain.dependencies {
+      // Correct dependency: Syncable interface is in the shared core domain
       implementation(projects.core.coreDomain)
+      // Also include frontend domain if needed (e.g., for frontend-specific models)
+      implementation(projects.frontend.core.domain)
 
       // Networking
       implementation(libs.ktor.client.core)