HS: DOM ref-eq + compound selector + DOM tree fixes

- hs-id= uses JS === for DOM elements (hs-ref-eq), = for scalars
- != operator now uses hs-id= for structural correctness
- compound tag[attr=val] selector matching in test runner
- dom-query-all replaces host-call querySelectorAll
- DOM tree structure corrected in 4 generated tests (elements were
  appended to wrong parents)

tests/playwright/generate-sx-tests.py

@@ -210,11 +210,18 @@ def parse_html(html):
     # button HTML in `properly processes hyperscript X` tests). HTMLParser handles
     # backslashes in attribute values as literal characters, so we leave them.
 
+    # HTML5 void elements — never have children, auto-pop from stack immediately.
+    VOID_TAGS = {'area','base','br','col','embed','hr','img','input','link',
+                 'meta','param','source','track','wbr'}
+
     elements = []
     stack = []
 
     class Parser(HTMLParser):
         def handle_starttag(self, tag, attrs):
+            # Pop any void elements left on the stack (they have no close tag).
+            while stack and stack[-1]['tag'] in VOID_TAGS:
+                stack.pop()
             el = {
                 'tag': tag, 'id': None, 'classes': [], 'hs': None,
                 'attrs': {}, 'inner': '', 'depth': len(stack),
@@ -244,6 +251,9 @@ def parse_html(html):
             elements.append(el)
 
         def handle_endtag(self, tag):
+            # Pop void elements first (they don't have close tags but may linger).
+            while stack and stack[-1]['tag'] in VOID_TAGS:
+                stack.pop()
             if stack and stack[-1]['tag'] == tag:
                 stack.pop()