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-steps/dto/create-step.dto.ts

@@ -0,0 +1,26 @@
+import { JobStepPhase, JobStepType, JobStepStatus } from "@prisma/client";
+import { IsString, IsEnum, IsInt, IsOptional, MinLength, MaxLength, Min } from "class-validator";
+
+/**
+ * DTO for creating a new job step
+ */
+export class CreateStepDto {
+  @IsInt({ message: "ordinal must be an integer" })
+  @Min(0, { message: "ordinal must be at least 0" })
+  ordinal!: number;
+
+  @IsEnum(JobStepPhase, { message: "phase must be a valid JobStepPhase" })
+  phase!: JobStepPhase;
+
+  @IsString({ message: "name must be a string" })
+  @MinLength(1, { message: "name must not be empty" })
+  @MaxLength(200, { message: "name must not exceed 200 characters" })
+  name!: string;
+
+  @IsEnum(JobStepType, { message: "type must be a valid JobStepType" })
+  type!: JobStepType;
+
+  @IsOptional()
+  @IsEnum(JobStepStatus, { message: "status must be a valid JobStepStatus" })
+  status?: JobStepStatus;
+}

apps/api/src/job-steps/dto/index.ts

@@ -0,0 +1,2 @@
+export * from "./create-step.dto";
+export * from "./update-step.dto";

apps/api/src/job-steps/dto/update-step.dto.ts

@@ -0,0 +1,25 @@
+import { JobStepStatus } from "@prisma/client";
+import { IsEnum, IsString, IsOptional, IsInt, Min } from "class-validator";
+
+/**
+ * DTO for updating a job step
+ */
+export class UpdateStepDto {
+  @IsOptional()
+  @IsEnum(JobStepStatus, { message: "status must be a valid JobStepStatus" })
+  status?: JobStepStatus;
+
+  @IsOptional()
+  @IsString({ message: "output must be a string" })
+  output?: string;
+
+  @IsOptional()
+  @IsInt({ message: "tokensInput must be an integer" })
+  @Min(0, { message: "tokensInput must be at least 0" })
+  tokensInput?: number;
+
+  @IsOptional()
+  @IsInt({ message: "tokensOutput must be an integer" })
+  @Min(0, { message: "tokensOutput must be at least 0" })
+  tokensOutput?: number;
+}