implement-feature-complete

Manages complete feature implementation lifecycle through 10 stages: planning, TDD, naming, DRY, implementation, refactor, integration testing, E2E testing, real usage validation, and production monitoring. Use when implementing new features, significant changes, or onboarding to project workflow. Ensures Clean Architecture, fail-fast principles, ServiceResult pattern, and quality gates. Triggers on "implement feature X", "add functionality Y", "complete workflow for Z", "end-to-end implementation", or "production-ready feature".