Function drop_embedding_tables 

pub async fn drop_embedding_tables(
    conn: &Connection,
    vec_conn: Option<&VecConnection>,
) -> Result<(), Error>

Drop embedding tables entirely for a full rebuild.

This is much faster than DELETE FROM for large tables — it avoids generating tombstone pages that bloat the database file. The caller must call ensure_schema + ensure_vec_schema afterwards to recreate the tables.