feat: fixup "setup seaorm and a first "debug" entity as example"

crates/backend/src/db.rs

@@ -0,0 +1,11 @@
+use migration::{Migrator, MigratorTrait};
+use sea_orm::{Database, DatabaseConnection, DbErr};
+use std::env;
+
+pub async fn get_connection() -> Result<DatabaseConnection, DbErr> {
+    let database_url = env::var("DATABASE_URL").expect("DATABASE_URL must be set");
+
+    let db_connection = Database::connect(database_url).await?;
+    Migrator::up(&db_connection, None).await?;
+    Ok(db_connection)
+}