feat(build): generate page-boundary helper

Expose generated ui::page as the canonical page-boundary rendering helper and move the Workout golden path and docs off beginner-visible ui::render calls.

req: public_api/002

req: codegen/002

req: canonical_authoring/006

examples/workout/src/lib.rs

@@ -627,7 +627,7 @@ pub struct AppShell {
 }
 
 pub fn page(runtime_src: &'static str, state: &WorkoutState) -> Html {
-    ui::render(&AppShell {
+    ui::page(&AppShell {
         runtime_src,
         body: render(state),
     })
@@ -683,7 +683,7 @@ pub fn view(state: &WorkoutState) -> Workout {
 }
 
 pub fn render(state: &WorkoutState) -> Html {
-    ui::render(&view(state))
+    ui::page(&view(state))
 }
 
 #[derive(Clone, Debug)]