Function app 

pub fn app(
    auth: Arc<IjimaAuth>,
    store: Arc<dyn Store>,
    kg: Arc<dyn KnowledgeGraph>,
    embedder: Option<Arc<dyn Embedder>>,
    redactor: Arc<Redactor>,
) -> Router

Builds the Ijima HTTP application router.

auth and store are shared via axum’s Extension layer; the AuthPrincipal extractor reads auth to verify bearer tokens.