🐛 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

frontend/static/js/main.js

@@ -125,7 +125,18 @@ window.documentApp = () => ({
         this.error = '';
         
         try {
-            this.documents = await window.api.getDocuments();
+            const allDocuments = await window.api.getDocuments();
+            
+            // HTML 문서만 필터링 (PDF 파일 제외)
+            this.documents = allDocuments.filter(doc => 
+                doc.html_path && 
+                doc.html_path.includes('/documents/')  // HTML은 documents 폴더에 저장됨
+            );
+            
+            console.log('📄 전체 문서:', allDocuments.length, '개');
+            console.log('📄 HTML 문서:', this.documents.length, '개');
+            console.log('📄 PDF 파일:', allDocuments.length - this.documents.length, '개 (제외됨)');
+            
             this.updateAvailableTags();
             this.filterDocuments();
             this.syncUIState(); // UI 상태 동기화