feat(API): 중간검사 문서 템플릿 동적 연동 - process_steps ↔ document_templates 연결

- process_steps 테이블에 document_template_id FK 추가 (migration)
- ProcessStep 모델에 documentTemplate BelongsTo 관계 추가
- ProcessStepService에서 documentTemplate eager loading
- StoreProcessStepRequest/UpdateProcessStepRequest에 document_template_id 유효성 검증
- WorkOrderService에 getInspectionTemplate(), createInspectionDocument() 메서드 추가
- WorkOrderController에 inspection-template/inspection-document 엔드포인트 추가
- DocumentService.formatTemplateForReact() 접근자 public으로 변경
- i18n 메시지 키 추가 (inspection_document_created, no_inspection_template)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Http/Requests/V1/ProcessStep/StoreProcessStepRequest.php

@@ -18,6 +18,7 @@ public function rules(): array
             'is_required' => ['nullable', 'boolean'],
             'needs_approval' => ['nullable', 'boolean'],
             'needs_inspection' => ['nullable', 'boolean'],
+            'document_template_id' => ['nullable', 'integer', 'exists:document_templates,id'],
             'is_active' => ['nullable', 'boolean'],
             'connection_type' => ['nullable', 'string', 'max:20'],
             'connection_target' => ['nullable', 'string', 'max:255'],
@@ -32,6 +33,7 @@ public function attributes(): array
             'is_required' => '필수여부',
             'needs_approval' => '승인필요여부',
             'needs_inspection' => '검사필요여부',
+            'document_template_id' => '문서양식',
             'is_active' => '사용여부',
             'connection_type' => '연결유형',
             'connection_target' => '연결대상',