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>

apps/api/src/job-events/dto/create-event.dto.ts

@@ -0,0 +1,20 @@
+import { IsString, IsOptional, IsObject, IsUUID, IsEnum } from "class-validator";
+import { EventType, ALL_EVENT_TYPES } from "../event-types";
+
+/**
+ * DTO for creating a job event
+ */
+export class CreateEventDto {
+  @IsEnum(ALL_EVENT_TYPES)
+  type!: EventType;
+
+  @IsString()
+  actor!: string;
+
+  @IsObject()
+  payload!: Record<string, unknown>;
+
+  @IsOptional()
+  @IsUUID()
+  stepId?: string;
+}