Make the Rust client the sole app

docs/CLIENT_CORE.md

@@ -1,6 +1,6 @@
-# `app-rust`'s `client` module
+# `app`'s `client` module
 
-`app-rust/src/client` contains platform- and UI-independent client logic. It
+`app/src/client` contains platform- and UI-independent client logic. It
 must not depend on iris; a `use iris::` below this directory is a layering
 defect. `event-model` remains a separate crate because the server and client
 both depend on that wire contract.
@@ -71,4 +71,4 @@ shared non-UI consumer needs them.
 
 Run `./scripts/run-tests.sh` from the repository root. For this crate alone,
 run `cargo test`, `cargo clippy --all-targets`, and `cargo fmt --check` from
-`app-rust/`.
+`app/`.