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>

database/migrations/2026_02_10_000001_add_document_template_id_to_process_steps.php

@@ -0,0 +1,27 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('process_steps', function (Blueprint $table) {
+            $table->foreignId('document_template_id')
+                ->nullable()
+                ->after('needs_inspection')
+                ->constrained('document_templates')
+                ->nullOnDelete();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('process_steps', function (Blueprint $table) {
+            $table->dropForeign(['document_template_id']);
+            $table->dropColumn('document_template_id');
+        });
+    }
+};