🐛 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/models/__init__.py

@@ -8,6 +8,10 @@ from .highlight import Highlight
 from .note import Note
 from .bookmark import Bookmark
 from .document_link import DocumentLink
+from .note_document import NoteDocument
+from .notebook import Notebook
+from .note_highlight import NoteHighlight
+from .note_note import NoteNote
 
 __all__ = [
     "User",
@@ -18,4 +22,8 @@ __all__ = [
     "Note",
     "Bookmark",
     "DocumentLink",
+    "NoteDocument",
+    "Notebook",
+    "NoteHighlight",
+    "NoteNote"
 ]