HS: fix empty/halt/morph/reset/dialog — 17 upstream tests pass

- parser `empty` no-target → (ref "me") (was bogus (sym "me"))
- parser `halt` modes distinguish: "all"/"bubbling"/"default" halt execution
  (raise hs-return), "the-event"/"the event's" only stop propagation/default.
  "'s" now matched as op token, not keyword.
- parser `get` cmd: dispatch + cmd-kw list + parse-get-cmd (parses expr with
  optional `as TYPE`). Required for `get result as JSON` in fetch chains.
- compiler empty-target for (local X): emit (set! X (hs-empty-like X)) so
  arrays/sets/maps clear the variable, not call DOM empty on the value.
- runtime hs-empty-like: container-of-same-type empty value.
- runtime hs-empty-target!: drop dead FORM branch that was short-circuiting
  to innerHTML=""; the querySelectorAll-over-inputs branch now runs.
- runtime hs-halt!: take ev param (was free `event` lookup); raise hs-return
  to stop execution unless mode is "the-event".
- runtime hs-reset!: type-aware — FORM → reset, INPUT/TEXTAREA → value/checked
  from defaults, SELECT → defaultSelected option.
- runtime hs-open!/hs-close!: toggle `open` attribute on details elements
  (not just the prop) so dom-has-attr? assertions work.
- runtime hs-coerce JSON: json-stringify dict/list (was str).
- test-runner mock: host-get on List + "length"/"size" (was only Dict);
  dom-set-attr tracks defaultChecked / defaultSelected / defaultValue;
  mock_query_all supports comma-separated selector groups.
- generator: emit boolean attrs (checked/selected/etc) even with null value;
  drop overcautious "skip HS with bare quotes or embedded HTML" guard so
  morph tests (source contains embedded <div>) emit properly.

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

lib/hyperscript/tokenizer.sx

@@ -183,7 +183,8 @@
     "focus"
     "blur"
     "dom"
-    "morph"))
+    "morph"
+    "using"))
 
 (define hs-keyword? (fn (word) (some (fn (k) (= k word)) hs-keywords)))