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>

routes/api/v1/documents.php

@@ -33,6 +33,7 @@
     Route::get('/{id}', [DocumentController::class, 'show'])->whereNumber('id')->name('v1.documents.show');
     Route::post('/', [DocumentController::class, 'store'])->name('v1.documents.store');
     Route::patch('/{id}', [DocumentController::class, 'update'])->whereNumber('id')->name('v1.documents.update');
+    Route::patch('/{id}/snapshot', [DocumentController::class, 'patchSnapshot'])->whereNumber('id')->name('v1.documents.snapshot');
     Route::delete('/{id}', [DocumentController::class, 'destroy'])->whereNumber('id')->name('v1.documents.destroy');
 
     // 결재 워크플로우