Add DDD Layer Placement Guide to Contributing Documentation

[josecelano]

Add DDD Layer Placement Guide to Contributing Documentation

📋 Issue Information

• Type: Documentation Enhancement
• Priority: High
• Related Issue: Move config module from domain to create command handler #75 - Move config module to correct DDD layer
• Parent Epic: None (standalone improvement)

🎯 Problem Statement

The project lacks clear guidelines on which code belongs in which DDD layer (Domain, Application, Infrastructure, Presentation). This has led to violations like the config module (#75) being placed in the domain layer when it clearly belongs in the application layer.

Without explicit documentation, contributors (including AI assistants) may:

• Place DTOs in the domain layer
• Mix infrastructure concerns (file I/O, HTTP) with domain logic
• Create unclear boundaries between layers
• Make code harder to maintain and test

💡 Proposed Solution

Create a comprehensive guide docs/contributing/ddd-layer-placement.md that clearly documents each layer's purpose, rules, red flags, examples, and includes a decision flowchart.

📝 Implementation Plan

See detailed specification: docs/issues/add-ddd-layer-placement-guide.md

✅ Acceptance Criteria

Note for Contributors: These criteria define what the PR reviewer will check. Use this as your pre-review checklist before submitting the PR to minimize back-and-forth iterations.

• Document created at docs/contributing/ddd-layer-placement.md
• All four layers documented with clear rules and examples
• Nuanced guidance on serde usage included (entities vs DTOs)
• Decision flowchart included for quick reference
• Real code examples from the codebase
• Linked from docs/contributing/README.md
• Referenced in .github/copilot-instructions.md
• All linters pass (markdownlint, cspell)
• Document follows project markdown conventions

🏷️ Labels

documentation, enhancement, DDD, contributing-guide