Function search_courses_by_slug_or_name 

pub async fn search_courses_by_slug_or_name(
    conn: &mut PgConnection,
    query: &str,
    limit: i64,
) -> ModelResult<Vec<Course>>

Finds courses by slug or (fuzzy) name for the support chatbot’s find_course tool. Exact slug matches rank first, then substring name matches, then trigram similarity to name.