docs: update for new crate layout

crates/application/src/users/resolve_username_to_id.rs

@@ -1,4 +1,4 @@
-//! Absorbs `handlers/users.rs::get_user_by_username`'s
+//! Absorbs `http-axum/src/html/users.rs::get_user_by_username`'s
 //! `repos.user.find_by_username()` call. `None` means "no such username" — the
 //! handler turns that into a 404, same as it always has; this is not an error
 //! condition.