feat(#168): Implement job steps tracking

Implement JobStepsModule for granular step tracking within runner jobs.

Features:
- Create and track job steps (SETUP, EXECUTION, VALIDATION, CLEANUP)
- Track step status transitions (PENDING → RUNNING → COMPLETED/FAILED)
- Record token usage for AI_ACTION steps
- Calculate step duration automatically
- GET endpoints for listing and retrieving steps

Implementation:
- JobStepsService: CRUD operations, status tracking, duration calculation
- JobStepsController: GET /runner-jobs/:jobId/steps endpoints
- DTOs: CreateStepDto, UpdateStepDto with validation
- Full unit test coverage (16 tests)

Quality gates:
- Build: ✅ Passed
- Lint: ✅ Passed
- Tests: ✅ 16/16 passed
- Coverage: ✅ 100% statements, 100% functions, 100% lines, 83.33% branches

Also fixed pre-existing TypeScript strict mode issue in job-events DTO.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/scratchpads/168-job-steps-tracking.md

@@ -0,0 +1,66 @@
+# Issue #168: Job steps tracking
+
+## Objective
+
+Implement job-steps module for granular step tracking within jobs. This module will track individual steps (SETUP, EXECUTION, VALIDATION, CLEANUP) within a runner job, recording status transitions, token usage, and duration.
+
+## Approach
+
+1. Analyze existing RunnerJobsModule and JobStep model
+2. Create JobStepsModule with TDD approach
+3. Implement service layer for step CRUD and status tracking
+4. Implement controller with GET endpoints
+5. Ensure proper integration with RunnerJobsModule
+
+## Progress
+
+- [x] Analyze existing code structure
+- [x] Create directory structure and DTOs
+- [x] RED: Write tests for JobStepsService
+- [x] GREEN: Implement JobStepsService
+- [x] RED: Write tests for JobStepsController
+- [x] GREEN: Implement JobStepsController
+- [x] Create JobStepsModule
+- [x] REFACTOR: Clean up and optimize
+- [x] Quality gates: typecheck, lint, test, coverage
+- [x] Commit changes
+
+## Testing
+
+- Unit tests for service methods (13 tests)
+- Unit tests for controller endpoints (3 tests)
+- Mock Prisma service
+- Verify token usage tracking
+- Verify duration calculation
+- Coverage: 100% statements, 100% functions, 100% lines, 83.33% branches
+
+## Notes
+
+- Step types: COMMAND, AI_ACTION, GATE, ARTIFACT
+- Step phases: SETUP, EXECUTION, VALIDATION, CLEANUP
+- Status transitions: pending → running → completed/failed
+- Track token usage per step (for AI_ACTION steps)
+- Calculate duration on completion
+
+## Implementation Summary
+
+Created the following files:
+
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/job-steps/job-steps.module.ts` - Module definition
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/job-steps/job-steps.service.ts` - Service with CRUD operations
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/job-steps/job-steps.controller.ts` - Controller with GET endpoints
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/job-steps/dto/create-step.dto.ts` - DTO for creating steps
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/job-steps/dto/update-step.dto.ts` - DTO for updating steps
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/job-steps/dto/index.ts` - DTO exports
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/job-steps/job-steps.service.spec.ts` - Service tests (13 tests)
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/job-steps/job-steps.controller.spec.ts` - Controller tests (3 tests)
+- `/home/jwoltje/src/mosaic-stack/apps/api/src/job-steps/index.ts` - Module exports
+
+Also fixed pre-existing issue in job-events DTO (added `!` to required properties).
+
+## Quality Gates
+
+- ✅ Build: Passed
+- ✅ Lint: Passed (auto-fixed formatting)
+- ✅ Tests: 16/16 passed
+- ✅ Coverage: 100% statements, 100% functions, 100% lines, 83.33% branches