Initialize RTGS prototype repository

3센터 A-A-A RTGS 실시간총액결제 프로토타입 최초 버전관리 시작.
- backend: Kotlin/Gradle 멀티모듈(sequencer, common, 채널/센터 모듈)
- frontend: Vite + TS
- infra: docker-compose, prometheus/grafana, ELK 네이티브 스크립트
- loadtest(k6), sim(장애/순서/정합성 시나리오), docs(PoC 보고서/복원력방안)

backend/common/build.gradle.kts

@@ -0,0 +1,29 @@
+plugins {
+    kotlin("jvm")
+    kotlin("plugin.jpa")   // all-open + no-arg for @Entity (Kotlin classes are final by default)
+    id("io.spring.dependency-management")
+}
+
+dependencyManagement {
+    imports {
+        mavenBom("org.springframework.boot:spring-boot-dependencies:3.3.4")
+    }
+}
+
+dependencies {
+    implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
+    implementation("com.fasterxml.jackson.dataformat:jackson-dataformat-xml")
+    // JPA annotations only (entities shared across ledger services); runtime provided by services.
+    compileOnly("jakarta.persistence:jakarta.persistence-api")
+    // 로그 -> Logstash(TCP json). 공유 logback-spring.xml과 함께 전 서비스에 전파(runtime).
+    implementation("net.logstash.logback:logstash-logback-encoder:7.4")
+    implementation("io.micrometer:micrometer-registry-prometheus") // 메트릭(B4)
+    // 하트비트 자동설정(B5) 컴파일용 — 런타임은 각 서비스가 제공
+    compileOnly("org.springframework.boot:spring-boot-autoconfigure")
+    compileOnly("org.springframework:spring-context")
+    compileOnly("org.springframework:spring-jdbc")
+    compileOnly("org.slf4j:slf4j-api")
+    testImplementation("org.jetbrains.kotlin:kotlin-test-junit5")
+    testImplementation("org.junit.jupiter:junit-jupiter")
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+}