HS: assignableElements — set vs put distinction (+8 tests)

Parser: parse-set-cmd now emits (set-el! target value) when target is
a query node (e.g. #id, .class), keeping (set! ...) for all other
targets.

Compiler: add (set-el! ...) handler that calls hs-set-element!; revert
emit-set for query targets back to hs-set-inner-html! so that
put "x" into #target keeps setting innerHTML rather than replacing
the element.

Runtime: hs-set-element! new function — parses value as HTML into a
temp div; if it contains element children, replaces the target element
via replaceChild and boots hyperscript on the new element; otherwise
falls through to hs-set-inner-html!. Removes the spurious
host-to-list wrapper that was causing len() to always return 0.

Result: all 8 assignableElements tests pass (set #id / set .class /
set closest / swap, plus put-into-still-works-as-innerHTML).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

spec/tests/test-hyperscript-behavioral.sx

@@ -3927,8 +3927,7 @@
       (dom-append (dom-body) _el-button)
       (hs-activate! _el-button)
       (dom-dispatch _el-button "click" nil)
-      (assert= (dom-text-content (dom-query-by-id "target")) "new")
-    ))
+      (assert= (dom-text-content (dom-query-by-id "target")) "new")))
   (deftest "set #id replaces element with HTML string"
     (hs-cleanup!)
     (let ((_el-target (dom-create-element "div")) (_el-button (dom-create-element "button")))