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/169-job-events-audit.md

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+# Issue #169: Job events and audit logging
+
+## Objective
+
+Implement job-events module for immutable audit logging using event sourcing pattern.
+
+## Approach
+
+1. Create module structure (module, service, controller, DTOs)
+2. Define event type constants
+3. Implement event emission and persistence (PostgreSQL)
+4. Add API endpoints for querying events
+5. Follow TDD: Write tests first, then implementation
+
+## Event Types
+
+- Job lifecycle: job.created, job.queued, job.started, job.completed, job.failed
+- Step lifecycle: step.started, step.progress, step.output, step.completed
+- AI events: ai.tool_called, ai.tokens_used, ai.artifact_created
+- Gate events: gate.started, gate.passed, gate.failed
+
+## Storage Strategy
+
+- PostgreSQL: Immutable audit log (permanent)
+- Valkey Streams: Deferred to future issue
+- Valkey Pub/Sub: Deferred to future issue
+
+## API Endpoints
+
+- GET /runner-jobs/:jobId/events - List events for a job
+- GET /runner-jobs/:jobId/events/stream - SSE stream (Phase 4, deferred)
+
+## Progress
+
+- [x] Create scratchpad
+- [x] Review existing schema (JobEvent model)
+- [x] Define event type constants
+- [x] Write tests for JobEventsService
+- [x] Implement JobEventsService
+- [x] Write tests for JobEventsController
+- [x] Implement JobEventsController
+- [x] Create JobEventsModule
+- [x] Register modules in app.module.ts
+- [x] Run quality gates (typecheck, lint, build, test)
+- [x] Commit changes
+
+## Testing
+
+- Unit tests for service (event emission, persistence, querying)
+- Unit tests for controller (endpoint behavior)
+- Target: >85% coverage
+
+Results:
+
+- JobEventsService: 13 tests passed
+- JobEventsController: 4 tests passed
+- Total: 17 tests passed
+- All quality gates passed (typecheck, lint, build, test)
+
+## Notes
+
+- Events are immutable once created
+- JobEvent model already exists in Prisma schema (from #164)
+- RunnerJobsModule available (from #167)
+- SSE streaming deferred to Phase 4
+
+## Implementation Details
+
+Files Created:
+
+- /apps/api/src/job-events/event-types.ts - Event type constants
+- /apps/api/src/job-events/dto/create-event.dto.ts - DTO for creating events
+- /apps/api/src/job-events/dto/query-events.dto.ts - DTO for querying events
+- /apps/api/src/job-events/dto/index.ts - DTO exports
+- /apps/api/src/job-events/job-events.service.ts - Event service implementation
+- /apps/api/src/job-events/job-events.service.spec.ts - Service tests (13 tests)
+- /apps/api/src/job-events/job-events.controller.ts - Event controller
+- /apps/api/src/job-events/job-events.controller.spec.ts - Controller tests (4 tests)
+- /apps/api/src/job-events/job-events.module.ts - Module definition
+- /apps/api/src/job-events/index.ts - Module exports
+
+Files Modified:
+
+- /apps/api/src/app.module.ts - Registered JobEventsModule
+
+Event Types Implemented:
+
+- Job lifecycle: job.created, job.queued, job.started, job.completed, job.failed, job.cancelled
+- Step lifecycle: step.started, step.progress, step.output, step.completed, step.failed
+- AI events: ai.tool_called, ai.tokens_used, ai.artifact_created
+- Gate events: gate.started, gate.passed, gate.failed
+
+API Endpoints:
+
+- GET /api/runner-jobs/:jobId/events - List events for a job (with pagination and filtering)
+
+Service Methods:
+
+- emitEvent() - Generic event emission
+- getEventsByJobId() - Query events with filters
+- Convenience methods: emitJobCreated(), emitJobStarted(), emitStepStarted(), emitAiTokensUsed(), etc.
+
+Quality Gates:
+
+- Typecheck: PASSED
+- Lint: PASSED
+- Build: PASSED
+- Tests: PASSED (17/17 tests)
+- Full test suite: PASSED (1327 tests)