Fix HTML attribute parsing: strip \" delimiters from JSON-extracted HTML

Tests with _=\"...\" attribute delimiters were garbled because
HTMLParser interpreted the backslash-quote as content, not delimiters.
Now html.replace('\"', '"') normalizes before parsing.

Fixes ~15 tests across toggle, transition, and other categories
that were previously running with corrupted HS source.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/playwright/generate-sx-tests.py

@@ -98,6 +98,9 @@ def parse_html(html):
     # Remove | separators
     html = html.replace(' | ', '')
 
+    # Fix escaped attribute delimiters from JSON extraction (\" → ")
+    html = html.replace('\\"', '"')
+
     elements = []
     stack = []