🐛 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/core/database.py

@@ -2,9 +2,9 @@
 데이터베이스 설정 및 연결
 """
 from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine, async_sessionmaker
-from sqlalchemy.orm import DeclarativeBase
-from sqlalchemy import MetaData
-from typing import AsyncGenerator
+from sqlalchemy.orm import DeclarativeBase, sessionmaker, Session
+from sqlalchemy import MetaData, create_engine
+from typing import AsyncGenerator, Generator
 
 from .config import settings
 
@@ -35,6 +35,15 @@ engine = create_async_engine(
     pool_recycle=300,
 )
 
+# 동기 데이터베이스 엔진 생성 (노트 API용)
+sync_database_url = settings.DATABASE_URL.replace("postgresql+asyncpg://", "postgresql://")
+sync_engine = create_engine(
+    sync_database_url,
+    echo=settings.DEBUG,
+    pool_pre_ping=True,
+    pool_recycle=300,
+)
+
 # 비동기 세션 팩토리
 AsyncSessionLocal = async_sessionmaker(
     engine,
@@ -42,9 +51,16 @@ AsyncSessionLocal = async_sessionmaker(
     expire_on_commit=False,
 )
 
+# 동기 세션 팩토리
+SyncSessionLocal = sessionmaker(
+    sync_engine,
+    class_=Session,
+    expire_on_commit=False,
+)
+
 
 async def get_db() -> AsyncGenerator[AsyncSession, None]:
-    """데이터베이스 세션 의존성"""
+    """비동기 데이터베이스 세션 의존성"""
     async with AsyncSessionLocal() as session:
         try:
             yield session
@@ -55,6 +71,18 @@ async def get_db() -> AsyncGenerator[AsyncSession, None]:
             await session.close()
 
 
+def get_sync_db() -> Generator[Session, None, None]:
+    """동기 데이터베이스 세션 의존성 (노트 API용)"""
+    session = SyncSessionLocal()
+    try:
+        yield session
+    except Exception:
+        session.rollback()
+        raise
+    finally:
+        session.close()
+
+
 async def init_db() -> None:
     """데이터베이스 초기화"""
     from ..models import user, document, highlight, note, bookmark