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>

tests/playwright/generate-sx-tests.py

@@ -125,8 +125,6 @@ SKIP_TEST_NAMES = {
     "can ignore when target doesn't exist",
     "can ignore when target doesn\\'t exist",
     "can handle an or after a from clause",
-    "supports \"elsewhere\" modifier",
-    "supports \"from elsewhere\" modifier",
     # upstream 'def' category — namespaced def + dynamic `me` inside callee
     "functions can be namespaced",
     "is called synchronously",