🐛 Fix Alpine.js SyntaxError and backlink visibility issues

- Fix SyntaxError in viewer.js line 2868 (.bind(this) issue in setTimeout)
- Resolve Alpine.js 'Can't find variable' errors (documentViewer, goBack, etc.)
- Fix backlink rendering and persistence during temporary highlights
- Add backlink protection and restoration mechanism in highlightAndScrollToText
- Implement Note Management System with hierarchical notebooks
- Add note highlights and memos functionality
- Update cache version to force browser refresh (v=2025012641)
- Add comprehensive logging for debugging backlink issues

backend/src/api/routes/document_links.py

@@ -402,6 +402,8 @@ class BacklinkResponse(BaseModel):
     source_document_id: str
     source_document_title: str
     source_document_book_id: Optional[str]
+    target_document_id: str  # 추가
+    target_document_title: str  # 추가
     selected_text: str
     start_offset: int
     end_offset: int
@@ -421,16 +423,21 @@ async def get_document_backlinks(
     db: AsyncSession = Depends(get_db)
 ):
     """문서의 백링크 조회 (이 문서를 참조하는 모든 링크)"""
+    print(f"🔍 백링크 API 호출됨 - 문서 ID: {document_id}, 사용자: {current_user.email}")
+    
     # 문서 존재 확인
     result = await db.execute(select(Document).where(Document.id == document_id))
     document = result.scalar_one_or_none()
     
     if not document:
+        print(f"❌ 문서를 찾을 수 없음: {document_id}")
         raise HTTPException(
             status_code=status.HTTP_404_NOT_FOUND,
             detail="Document not found"
         )
     
+    print(f"✅ 문서 찾음: {document.title}")
+    
     # 권한 확인
     if not document.is_public and document.uploaded_by != current_user.id and not current_user.is_admin:
         raise HTTPException(
@@ -454,12 +461,20 @@ async def get_document_backlinks(
     result = await db.execute(query)
     backlinks = []
     
+    print(f"🔍 백링크 쿼리 실행 완료")
+    
     for link, source_doc, book in result.fetchall():
+        print(f"📋 백링크 발견: {source_doc.title} -> {document.title}")
+        print(f"   - 선택된 텍스트: {link.selected_text}")
+        print(f"   - 링크 타입: {link.link_type}")
+        
         backlinks.append(BacklinkResponse(
             id=str(link.id),
             source_document_id=str(link.source_document_id),
             source_document_title=source_doc.title,
             source_document_book_id=str(book.id) if book else None,
+            target_document_id=str(link.target_document_id),  # 추가
+            target_document_title=document.title,  # 추가
             selected_text=link.selected_text,
             start_offset=link.start_offset,
             end_offset=link.end_offset,
@@ -469,6 +484,7 @@ async def get_document_backlinks(
             created_at=link.created_at.isoformat()
         ))
     
+    print(f"✅ 총 {len(backlinks)}개의 백링크 반환")
     return backlinks