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

build.gradle

@@ -0,0 +1,60 @@
+plugins {
+    id 'java'
+    id 'org.springframework.boot' version '3.2.5' apply false
+    id 'io.spring.dependency-management' version '1.1.4' apply false
+}
+
+allprojects {
+    group = 'com.ga'
+    version = '1.0.0-alpha'
+
+    repositories {
+        mavenCentral()
+    }
+}
+
+subprojects {
+    apply plugin: 'java'
+    apply plugin: 'java-library'
+    apply plugin: 'io.spring.dependency-management'
+
+    java {
+        toolchain {
+            languageVersion = JavaLanguageVersion.of(17)
+        }
+    }
+
+    compileJava {
+        options.encoding = 'UTF-8'
+        options.compilerArgs << '-parameters'
+    }
+
+    compileTestJava {
+        options.encoding = 'UTF-8'
+    }
+
+    dependencyManagement {
+        imports {
+            mavenBom org.springframework.boot.gradle.plugin.SpringBootPlugin.BOM_COORDINATES
+        }
+    }
+
+    dependencies {
+        // Lombok
+        compileOnly 'org.projectlombok:lombok'
+        annotationProcessor 'org.projectlombok:lombok'
+        testCompileOnly 'org.projectlombok:lombok'
+        testAnnotationProcessor 'org.projectlombok:lombok'
+
+        // MapStruct
+        implementation 'org.mapstruct:mapstruct:1.5.5.Final'
+        annotationProcessor 'org.mapstruct:mapstruct-processor:1.5.5.Final'
+
+        // Test
+        testImplementation 'org.springframework.boot:spring-boot-starter-test'
+    }
+
+    test {
+        useJUnitPlatform()
+    }
+}