Fix SQLAlchemy 2.0 compatibility

- Wrap PRAGMA statement with text() for SQLAlchemy 2.0
- Fixes ObjectNotExecutableError on database initialization

backend/app/database.py

@@ -10,6 +10,7 @@ from sqlalchemy import (
     DateTime,
     Index,
     CheckConstraint,
+    text,
 )
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import sessionmaker
@@ -101,7 +102,7 @@ def init_db():
     # Enable WAL mode for SQLite
     if "sqlite" in DATABASE_URL:
         with engine.connect() as conn:
-            conn.execute("PRAGMA journal_mode=WAL")
+            conn.execute(text("PRAGMA journal_mode=WAL"))
             conn.commit()
 
     # Initialize statistics table with single row