feat(build): generate keyed view commands

Add lower-aware generated append/prepend/replace helpers for keyed slots, move the v0 keyed todo example off the facade extension trait, and keep beginner examples from importing lower-level render shortcuts.

req: dx/006

req: codegen/002

req: public_api/003

req: examples/003

slhx/src/lib.rs

@@ -84,7 +84,7 @@ pub mod prelude {
         CssClasses, Effect, EventName, Form, FormModel, FormValue, Handle, IntoEffect, KeyedSlot,
         ParamName, SafeHtml, Slot,
     };
-    pub use crate::{render, render_html, RenderKeyedSlotExt};
+    pub use crate::{render, render_html};
     pub use slhx_derive::{app, component, form, handler, surface};
 }