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.

.claude/skills/ddd-implement/SKILL.md

@@ -0,0 +1,66 @@
+# DDD Implementation Skill
+
+**Skill Name**: `ddd-implement`
+**Aliases**: `implement`, `ddd-code`
+**Version**: 1.0.0
+
+## Description
+
+Senior DDD developer that implements domain-driven code following Clean Architecture principles. Understands tactical DDD patterns, layer boundaries, and language-specific conventions.
+
+## Usage
+
+```bash
+/ddd-implement [--lang=go|java] [file-or-description]
+```
+
+**Examples**:
+```bash
+# Implement a specific aggregate
+/ddd-implement --lang=java "Implement Order aggregate with addLineItem and cancel methods"
+
+# Implement in existing file
+/ddd-implement --lang=go internal/domain/account/account.go
+
+# Implement use case
+/ddd-implement --lang=java "Implement TransferMoney use case in application layer"
+
+# Implement repository
+/ddd-implement --lang=go "Implement PostgreSQL repository for Account aggregate"
+```
+
+## Capabilities
+
+This skill can:
+- ✅ Implement **Aggregates** with proper invariant enforcement
+- ✅ Implement **Value Objects** with validation
+- ✅ Implement **Entities** (child entities within aggregates)
+- ✅ Implement **Use Cases** in application layer
+- ✅ Implement **Repositories** (interface + implementation)
+- ✅ Implement **Domain Events**
+- ✅ Follow **Error Handling** patterns (Result types for Java, errors for Go)
+- ✅ Respect **Layer boundaries** (domain, application, infrastructure)
+- ✅ Enforce **DDD rules** (aggregate boundaries, invariants, etc.)
+
+## What This Skill Does NOT Do
+
+- ❌ **Modeling/Design** - Use `/ddd-model` skill for that
+- ❌ **Infrastructure concerns** - Only implements adapters, not databases/HTTP servers themselves
+- ❌ **Tests** - Focuses on implementation (you can ask for tests separately)
+
+## System Prompt
+
+<system-prompt src="./system-prompt.md" />
+
+## Language Detection
+
+The skill detects language in this order:
+1. `--lang=` flag
+2. File extension (`.go`, `.java`)
+3. Current working directory structure
+4. Ask user if unclear
+
+## Related Skills
+
+- **ddd-model** - For domain modeling and design
+- **review** - For code review with DDD principles