[Task]: Implement relationships/dependencies between tasks

[luizhcastro]

Objective

Implement a system to create and manage dependencies/relationships between tasks. This includes defining dependency types (blocks, blocked by, relates to), ensuring dependency integrity, and providing APIs to query task relationships.

Scope

In scope:

• Create task_relationships entity with relationship types (blocks, blocked_by, relates_to, duplicates, parent_of, child_of)
• API endpoints to add/remove task relationships
• GET /api/tasks/:id/dependencies to retrieve all relationships
• Validation to prevent circular dependencies
• Cascade handling when tasks are deleted
• Support for querying blocked/blocking tasks

Out of scope:

• Gantt chart or timeline visualization
• Automatic dependency resolution
• Critical path calculation
• Dependency notifications (separate issue)

Acceptance criteria

• task_relationships entity created with all relationship types
• POST /api/tasks/:id/relationships endpoint to create relationship
• DELETE /api/tasks/:id/relationships/:relationshipId endpoint
• GET /api/tasks/:id/dependencies returning all related tasks
• Circular dependency validation implemented
• Cascading delete handling when tasks are removed
• Can query tasks blocked by a specific task
• Can query tasks blocking a specific task
• Unit tests covering all relationship types
• API documentation updated

Deadline (optional)

No response