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

.gitignore

@@ -0,0 +1,37 @@
+# Gradle
+.gradle/
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!gradle/wrapper/gradle-wrapper.properties
+
+# IDE
+.idea/
+*.iml
+*.iws
+.vscode/
+.settings/
+.project
+.classpath
+.factorypath
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Logs
+logs/
+*.log
+
+# Node
+node_modules/
+dist/
+.pnpm-store/
+
+# Env
+.env
+.env.local
+*.local
+
+# Build outputs
+out/
+target/