Function sync_fts_after_update 

pub fn sync_fts_after_update(
    conn: &Connection,
    memory_id: i64,
    old_name: &str,
    old_desc: &str,
    old_body: &str,
    new_name: &str,
    new_desc: &str,
    new_body: &str,
) -> Result<(), AppError>

Syncs FTS5 external-content index after an UPDATE on the memories table.

The AFTER UPDATE trigger (trg_fts_au) is intentionally absent because sqlite-vec loaded via sqlite3_auto_extension conflicts with FTS5 inside UPDATE triggers. This function performs the equivalent sync in Rust: DELETE the old entry, then INSERT the new one (external-content FTS5 tables do not support in-place UPDATE).