HS: keyword-as-ref fallback + list innerHTML join

- parse-atom: unrecognized keywords (e.g. index) fall back to ref,
  fixing 'set index to N' parse failure
- hs-set-inner-html!: join list values as "" so 'put [A,C] into el'
  concatenates strings not [object Object]

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

lib/hyperscript/runtime.sx

@@ -311,7 +311,9 @@
     hs-set-inner-html!
     (fn
       (target value)
-      (do (dom-set-inner-html target value) (hs-boot-subtree! target))))
+      (let
+        ((str-val (if (list? value) (join "" (map (fn (x) (str x)) value)) value)))
+        (do (dom-set-inner-html target str-val) (hs-boot-subtree! target)))))
   (define
     hs-put!
     (fn