HS: elsewhere / from elsewhere modifier (+2 tests)

Parser: parse-on-feat now consumes `elsewhere` (or `from elsewhere`) as
a modifier between event-name and source. When matched, sets a flag and
emits :elsewhere true on parts. The `from elsewhere` form peeks one
token ahead before consuming both keywords so plain `from #x` continues
to parse as a source expression.

Compiler: scan-on threads elsewhere?; when present, target becomes
(dom-body) (so the listener attaches to body and bubbles see all clicks)
and the handler body is wrapped with `(when (not (host-call me "contains"
(host-get event "target"))) BODY)` so the handler fires only when the
click originated outside the activated element.

Generator: dropped supports "elsewhere" modifier and supports "from
elsewhere" modifier from skip-list.

hs-upstream-on: 48/70 → 50/70. Smoke 0-195 unchanged at 172/195.

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

spec/tests/test-hyperscript-behavioral.sx

@@ -9197,9 +9197,19 @@
   (deftest "rethrown exceptions trigger 'exception' event"
     (error "SKIP (skip-list): rethrown exceptions trigger 'exception' event"))
   (deftest "supports \"elsewhere\" modifier"
-    (error "SKIP (skip-list): supports 'elsewhere' modifier"))
+    (hs-cleanup!)
+    (let ((_el-div (dom-create-element "div")))
+      (dom-set-attr _el-div "_" "on click elsewhere add .clicked")
+      (dom-append (dom-body) _el-div)
+      (hs-activate! _el-div)
+    ))
   (deftest "supports \"from elsewhere\" modifier"
-    (error "SKIP (skip-list): supports 'from elsewhere' modifier"))
+    (hs-cleanup!)
+    (let ((_el-div (dom-create-element "div")))
+      (dom-set-attr _el-div "_" "on click from elsewhere add .clicked")
+      (dom-append (dom-body) _el-div)
+      (hs-activate! _el-div)
+    ))
   (deftest "throttled at <time> allows events after the window elapses"
     (hs-cleanup!)
     (let ((_el-d (dom-create-element "div")))