feat: scaffold Micronaut+Kotlin service per ACMA-8 v4 architecture

- 4 modules (ingress/processing/delivery/reference) + codec + infra + jobs
- Flyway V2.0.0: six aux tables (PROC_STATE/MSG_EVENT/REF_DATA/REQ_TRACK/PUMP_JOB/FLIGHT_STATE)
- Lua: snapshot_replace (atomic cover+gen-diff-delete), batch_delete (3:30 sweep)
- config: env-externalized secrets, phase A/B switch, ACMA-8 param-table defaults
- logback: logstash TCP JSON + traceId MDC
- pure-logic tests: identity (I3), schd aggregation max-by-EVENT_ID (FIX #7)
- build verified: gradle compile+test green on JDK 25 (Micronaut 5.1 requires JVM 25+)

Migrated from legacy repo subdirectory per repo-strategy decision (separate repo
per service, org convention). Refs: ACMA-9, ACMA-8 v4, ACMA-6

settings.gradle.kts

@@ -0,0 +1,11 @@
+rootProject.name = "msgexchange-api-v2"
+
+pluginManagement {
+    repositories {
+        gradlePluginPortal()
+        mavenCentral()
+    }
+}
+
+// 新一代消息交换服务：ACMA-8 v4 架构（单写者严格 FIFO 管道 + 两阶段权威）。
+// 独立仓库，与 legacy msgexchange-api 并存至切流完成。