Refactor: Replace requirements domain with research papers domain

[Brad-Edwards]

Description

Replace the existing requirements management domain with a research papers domain. This involves removing the current Requirement, RequirementRelation, and TraceabilityLink entities and introducing Paper, Citation, and ResearchLink entities.

Scope

• Remove existing domain entities: Requirement, RequirementRelation, TraceabilityLink
• Create new domain entities:
  • Paper: Represents a research paper with metadata (title, authors, abstract, DOI, publication date, etc.)
  • Citation: Represents a citation relationship between papers (citing paper, cited paper, context)
  • ResearchLink: Represents a link between research artifacts (papers, experiments, notes)
• Create corresponding repositories, services, and API controllers
• Update domain events and listeners
• Ensure ArchUnit rules still pass with new domain structure

Acceptance Criteria

• Old requirement entities are removed
• Paper entity with full CRUD operations
• Citation entity linking papers together
• ResearchLink entity for cross-domain references
• All ArchUnit architecture tests pass
• Unit tests for new domain entities and services