Function fts_search 

pub fn fts_search(
    conn: &Connection,
    query: &str,
    namespace: &str,
    memory_type: Option<&str>,
    limit: usize,
) -> Result<Vec<MemoryRow>, AppError>

Executes a prefix-matching FTS5 search against fts_memories.

The supplied query is suffixed with * to enable prefix matching, then joined back to memories to materialize full rows filtered by namespace.

Errors

Returns Err(AppError::Database) on any rusqlite failure.