Use one standard Iris resource bundle

docs/RUST.md

@@ -13,10 +13,12 @@ open work and measured constraints that are expensive to rediscover.
   Platform services are exposed to shared UI through small traits.
 - `iris/` is only a UI framework. Session, transcript, server, setup, and
   product styling concepts never belong there.
-- `iris/src/rsc` groups resources carried by or installed through `AppRsc`:
+- `iris/src/rsc` groups resources carried by or installed through `StdRsc`:
   attributes, events, overlays, pointer sensing/input, tasks, and per-widget
-  state. `widget/` is reserved for concrete retained widgets. Public paths
-  such as `iris::sense` remain aliases for readability.
+  state. It is the standard bundle used by Iris's hosts, not a requirement;
+  shared widgets depend on its narrow resource traits so a custom bundle can
+  implement only what it needs. `widget/` is reserved for concrete retained
+  widgets. Public paths such as `iris::sense` remain aliases for readability.
 - Phone and desktop layouts may differ. Their component implementations,
   colors, spacing, text styles, gestures, folding, and network behavior do
   not.