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-test/tests/examples_contract.rs

@@ -67,6 +67,7 @@ fn canonical_examples_do_not_author_low_level_resource_plumbing() {
         "InteractionForm",
         "register_handle(",
         "RenderSlotExt",
+        "RenderKeyedSlotExt",
         ".render(&",
         ".html(ui::render",
         ".html(slhx::render",