refactor: massive rename dap -> dat

- Renamed packages io.shinhanlife.dap to io.shinhanlife.dat
- Renamed modules dap-was-* and dap-gateway to dat-was-* and dat-gateway
- Renamed classes DapGateway* to DatGateway*
- Updated all references

dat-was-cus/build.gradle

@@ -0,0 +1,10 @@
+plugins {
+    // OTH Tool Pod를 독립 실행 가능한 Spring Boot JAR로 생성합니다.
+    id 'org.springframework.boot'
+}
+
+dependencies {
+    // MCP Server, Tool 공통 처리, MCI/EAI 연동 기반은 dat-was-lib에서 상속합니다.
+    implementation project(':dat-was-lib')
+    implementation 'org.apache.poi:poi-ooxml:5.3.0'
+}