HS: in-expression filter semantics (+1 test)

`1 in [1, 2, 3]` must return (list 1) not true. Root cause: in? compiled
to hs-contains? which returns boolean for scalar items. Fix: new hs-in?
returns filtered list; new in-bool? operator for is/am-in comparison
contexts so those still return boolean. Parser generates in-bool? for
`X is in Y` / `X am in Y`; plain `in` keeps in? → list return.

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

lib/hyperscript/runtime.sx

@@ -1535,6 +1535,25 @@
                 (hs-contains? (rest collection) item))))))
       (true false))))
 
+(define
+  hs-in?
+  (fn
+    (collection item)
+    (cond
+      ((nil? collection) (list))
+      ((list? collection)
+        (cond
+          ((nil? item) (list))
+          ((list? item)
+            (filter (fn (x) (hs-contains? collection x)) item))
+          ((hs-contains? collection item) (list item))
+          (true (list))))
+      (true (list)))))
+
+(define
+  hs-in-bool?
+  (fn (collection item) (not (hs-falsy? (hs-in? collection item)))))
+
 (define
   hs-is
   (fn