feat(build): add lower-aware put helper

Generate ui::put(slot, view) for lower-aware slot HTML updates and move examples/docs/contracts to that ergonomic path instead of hand-composing slot.html(render(...)).

req: dx/006

req: component/003

req: runtime/001

req: examples/003

examples/techdemo/src/lib.rs

@@ -30,7 +30,7 @@ mod tests {
     fn techdemo_uses_generated_slots_for_multi_target_updates() {
         fn update() -> impl IntoEffect {
             (
-                slots::hero_metrics.html(super::ui::render(&FastMetric { label: "fast" })),
+                super::ui::put(slots::hero_metrics, &FastMetric { label: "fast" }),
                 slots::notice.text("typed"),
             )
         }