Function feature_enabled 

pub async fn feature_enabled(db: &Db, key: &str) -> bool

true when the named flag is set and enabled = TRUE. Missing keys read as false. Reads go through a 60-second per-key cache so hot paths stay cheap.

Stability: the key is the public contract between project code and the operator. Treat key strings as snake_case identifiers (e.g. "new_signup_flow") — the table accepts any TEXT, but a stable convention makes the admin UI legible.