feat: [문서스냅샷] Lazy Snapshot API - snapshot 엔드포인트 + resolve에 snapshot_document_id 추가

- PATCH /documents/{id}/snapshot: canEdit 체크 없이 rendered_html만 업데이트
- DocumentService::patchSnapshot() 메서드 추가
- WorkOrderService::resolveInspectionDocument()에 snapshot_document_id 반환 (상태 무관, rendered_html NULL인 문서)

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

app/Services/WorkOrderService.php

@@ -2431,11 +2431,26 @@ public function resolveInspectionDocument(int $workOrderId, array $params = []):
             ->latest()
             ->first();
 
+        // Lazy Snapshot 대상: rendered_html이 없는 문서 (상태 무관)
+        $snapshotDocumentId = null;
+        $snapshotCandidate = Document::query()
+            ->where('tenant_id', $tenantId)
+            ->where('template_id', $templateId)
+            ->where('linkable_type', 'work_order')
+            ->where('linkable_id', $workOrderId)
+            ->whereNull('rendered_html')
+            ->latest()
+            ->value('id');
+        if ($snapshotCandidate) {
+            $snapshotDocumentId = $snapshotCandidate;
+        }
+
         return [
             'work_order_id' => $workOrderId,
             'template_id' => $templateId,
             'template' => $formattedTemplate,
             'existing_document' => $existingDocument,
+            'snapshot_document_id' => $snapshotDocumentId,
             'work_order_info' => $this->buildWorkOrderInfo($workOrder),
         ];
     }