feat(slhx): prefer render methods for views

Move view rendering onto Slot::render and KeyedSlot append/prepend/replace extension methods, leaving explicit text/html methods for non-view escape hatches.

req: codegen/002

req: view/001

examples/techdemo/src/lib.rs

@@ -28,7 +28,7 @@ mod tests {
     fn techdemo_uses_generated_slots_for_multi_target_updates() {
         fn update() -> impl IntoEffect {
             (
-                ui::control_center::slots::hero_metrics.render_view(&FastMetric { label: "fast" }),
+                ui::control_center::slots::hero_metrics.render(&FastMetric { label: "fast" }),
                 ui::control_center::slots::notice.text("typed"),
             )
         }