New link types added:
- depends_on: Task depends on another task to complete first
- needs: Task needs another task (weaker dependency)
- implements: Task implements a feature/requirement
- fixes: Task fixes an issue identified in another task
- causes: Task causes/introduces issue in another task
- subtask_of: Task is a subtask of another (parent-child)
Preserves existing types: blocks, relates_to, duplicates
Changes:
- Migration 021 updates database constraint
- Updated TypeScript types and MCP tool schema
- Applied to production database
Implements CF-385
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>