story: export generated DTOs to OpenAPI schemas

[soulcodingmatt]

Story

As a backend developer using Equilibrium, I want to export my generated DTOs to OpenAPI schema definitions, so that I can maintain API contracts without a separate OpenAPI-first workflow.

Context

Parent epic: #18

This is the core story of the OpenAPI export feature. It covers generating .yaml schema files from @GenerateDto-annotated source classes. The generated schemas should reflect the DTO field structure, types, and validation constraints.

The OpenAPI generation should ideally be a separate module/project that can be used standalone or integrated with Equilibrium.

Acceptance Criteria

• Given a class annotated with @GenerateDto, when the annotation processor runs, then a corresponding OpenAPI schema .yaml file is generated
• Given a DTO with primitive, String, and common Java types, when exported, then the schema maps types correctly to OpenAPI types
• Given a DTO with nested object references, when exported, then the schema uses $ref to reference other schemas
• Given a DTO with validation annotations, when exported, then the schema includes corresponding constraints (min, max, pattern, etc.)
• The export can be enabled/disabled via a processor option

Out of Scope (covered by other stories)

• Versioning and breaking change detection (epic: OpenAPI export functionality #18 scope)
• OAS project integration and push workflow (epic: OpenAPI export functionality #18 scope)
• Record and VO export evaluation (epic: OpenAPI export functionality #18 scope)

Acceptance Criteria

TODO: Define acceptance criteria for this story.

Acceptance Criteria

TODO: Define acceptance criteria for this story.