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-common/build.gradle

@@ -0,0 +1,36 @@
+// ga-common: 공통 프레임워크 (다른 모듈이 의존)
+bootJar.enabled = false
+jar.enabled = true
+
+dependencies {
+    api 'org.springframework.boot:spring-boot-starter-web'
+    api 'org.springframework.boot:spring-boot-starter-aop'
+    api 'org.springframework.boot:spring-boot-starter-security'
+    api 'org.springframework.boot:spring-boot-starter-validation'
+    api 'org.springframework.boot:spring-boot-starter-data-redis'
+    api 'org.springframework.boot:spring-boot-starter-cache'
+
+    // MyBatis
+    api 'org.mybatis.spring.boot:mybatis-spring-boot-starter:3.0.3'
+    api 'com.github.pagehelper:pagehelper-spring-boot-starter:2.1.0'
+
+    // PostgreSQL + Flyway
+    api 'org.postgresql:postgresql'
+    api 'org.flywaydb:flyway-core'
+
+    // JWT
+    api 'io.jsonwebtoken:jjwt-api:0.12.5'
+    runtimeOnly 'io.jsonwebtoken:jjwt-impl:0.12.5'
+    runtimeOnly 'io.jsonwebtoken:jjwt-jackson:0.12.5'
+
+    // Excel
+    api 'org.apache.poi:poi-ooxml:5.2.5'
+    api 'com.monitorjbl:xlsx-streamer:2.2.0'
+
+    // OpenAPI / Swagger
+    api 'org.springdoc:springdoc-openapi-starter-webmvc-ui:2.3.0'
+
+    // Commons
+    api 'org.apache.commons:commons-lang3'
+    api 'commons-io:commons-io:2.15.1'
+}