HS: send can reference sender (+1 test)

Three-part fix: (a) emit-send now builds detail=(dict "sender" me) on
(send NAME target) and bare (send NAME) instead of nil, so the receiving
handler has access to the sending element. (b) parser parse-atom now
recognises the `sender` keyword (previously swallowed as noise) and
emits it as (sender). (c) compiler translates bare `sender` symbol and
(sender) list-head to (hs-sender event) — a new runtime helper that
reads (get (host-get event "detail") "sender").

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/hyperscript/runtime.sx

@@ -687,6 +687,14 @@
           (dom-insert-adjacent-html target "beforeend" (str value)))
         (true nil)))))
 ;; Property-based is — check obj.key truthiness
+(define
+  hs-sender
+  (fn
+    (event)
+    (let
+      ((detail (host-get event "detail")))
+      (if detail (host-get detail "sender") nil))))
+;; Array slicing (inclusive both ends)
 (define
   hs-host-to-sx
   (fn
@@ -740,7 +748,7 @@
                           (dict-set! out k (hs-host-to-sx (host-get v k))))
                         (host-call (host-global "Object") "keys" v))
                       out)))))))))))
-;; Array slicing (inclusive both ends)
+;; Collection: sorted by
 (define
   hs-fetch
   (fn
@@ -750,7 +758,7 @@
       (let
         ((raw (perform (list "io-fetch" url fmt))))
         (cond ((= fmt "json") (hs-host-to-sx raw)) (true raw))))))
-;; Collection: sorted by
+;; Collection: sorted by descending
 (define
   hs-json-escape
   (fn
@@ -781,7 +789,7 @@
         (walk)
         out)
       "\"")))
-;; Collection: sorted by descending
+;; Collection: split by
 (define
   hs-json-stringify
   (fn
@@ -815,7 +823,7 @@
                   ks)))
             "}")))
       (true (hs-json-escape (str v))))))
-;; Collection: split by
+;; Collection: joined by
 (define
   hs-coerce
   (fn
@@ -929,7 +937,7 @@
           (map (fn (k) (list k (get value k))) (keys value))
           value))
       (true value))))
-;; Collection: joined by
+
 (define
   hs-gather-form-nodes
   (fn