feat: project skeleton + DB migrations V1-V12 + ga-common framework

- Gradle multi-module: ga-common, ga-core, ga-api, ga-batch, ga-admin
- Flyway V1-V12: org/product/rule/receive/ledger/settle/batch/code/menu/system + seed
- ga-common (complete):
  - model: ApiResponse, PageResponse, SearchParam, TreeNode
  - exception: ErrorCode, BizException, GlobalExceptionHandler
  - annotation + aop: @RequirePermission, @DataChangeLog, ApiLog
  - auth + security: JWT, SecurityConfig
  - mybatis: BaseMapper, EncryptTypeHandler, JsonTypeHandler, AuditInterceptor
  - code (Redis cached) / menu (RBAC tree) / file / system / notification
  - excel: SXSSF+Cursor export, SAX+batch import (1M/700K rows)
  - util: Date/Money/Mask/Encrypt/Security

ga-api/build.gradle

@@ -0,0 +1,13 @@
+// ga-api: REST API (실행 모듈)
+apply plugin: 'org.springframework.boot'
+
+bootJar {
+    enabled = true
+    archiveFileName = 'ga-api.jar'
+    mainClass = 'com.ga.api.GaApiApplication'
+}
+jar.enabled = false
+
+dependencies {
+    implementation project(':ga-core')
+}

ga-api/src/main/java/com/ga/api/GaApiApplication.java

@@ -0,0 +1,15 @@
+package com.ga.api;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+/**
+ * GA 수수료 정산 API 서버.
+ * 컴포넌트 스캔: com.ga 패키지 (common/core/api 모두 포함)
+ */
+@SpringBootApplication(scanBasePackages = {"com.ga"})
+public class GaApiApplication {
+    public static void main(String[] args) {
+        SpringApplication.run(GaApiApplication.class, args);
+    }
+}

ga-api/src/main/resources/application.yml

@@ -0,0 +1,56 @@
+spring:
+  application:
+    name: ga-api
+  profiles:
+    active: local
+  datasource:
+    url: jdbc:postgresql://localhost:5432/ga
+    username: ga
+    password: ga
+    driver-class-name: org.postgresql.Driver
+  flyway:
+    enabled: true
+    locations: classpath:db/migration
+    baseline-on-migrate: true
+  data:
+    redis:
+      host: localhost
+      port: 6379
+  servlet:
+    multipart:
+      max-file-size: 100MB
+      max-request-size: 100MB
+
+server:
+  port: 8080
+  servlet:
+    encoding:
+      charset: UTF-8
+      force: true
+
+mybatis:
+  config-location: classpath:mybatis/mybatis-config.xml
+  mapper-locations: classpath*:mapper/**/*.xml
+  type-aliases-package: com.ga.core.vo,com.ga.common.model
+
+pagehelper:
+  helper-dialect: postgresql
+  reasonable: true
+  support-methods-arguments: true
+
+springdoc:
+  swagger-ui:
+    path: /swagger-ui.html
+
+ga:
+  jwt:
+    secret: ${JWT_SECRET:change-me-please-this-must-be-at-least-256-bits-long-secret-key}
+    access-token-expire: 7200000
+    refresh-token-expire: 604800000
+  encrypt:
+    key: ${ENCRYPT_KEY:0123456789abcdef0123456789abcdef}
+
+logging:
+  level:
+    com.ga: DEBUG
+    org.mybatis: INFO