feat: add Spring Boot ERP application with user management domain

Implement DDD-based architecture with domain, application, infrastructure,
and API layers. Includes user/role management with authentication,
RBAC permissions, audit logging, Liquibase migrations, and test suite.

.gitignore

@@ -0,0 +1,52 @@
+# Compiled class files
+*.class
+target/
+out/
+
+# Log files
+*.log
+logs/
+
+# IDE files
+.idea/
+*.iml
+*.iws
+*.ipr
+.vscode/
+.classpath
+.project
+.settings/
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Package Files
+*.jar
+*.war
+*.nar
+*.ear
+*.zip
+*.tar.gz
+*.rar
+
+# Spring Boot
+spring-boot-devtools.properties
+
+# Environment variables
+.env
+.env.local
+
+# Database
+*.db
+*.sqlite
+
+# Test coverage
+.coverage
+htmlcov/
+coverage/
+
+# Maven
+.mvn/
+mvnw
+mvnw.cmd