fix(db): activer PRAGMA foreign_keys=ON pour SQLite (ON DELETE CASCADE effectif)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/database.py

@@ -1,9 +1,17 @@
 from sqlmodel import SQLModel, create_engine, Session
+from sqlalchemy import event
 from app.config import DATABASE_URL
 
 engine = create_engine(DATABASE_URL, connect_args={"check_same_thread": False})
 
 
+@event.listens_for(engine, "connect")
+def set_sqlite_pragma(dbapi_connection, connection_record):
+    cursor = dbapi_connection.cursor()
+    cursor.execute("PRAGMA foreign_keys=ON")
+    cursor.close()
+
+
 def get_session():
     with Session(engine) as session:
         yield session