Two related fixes for content being stripped by the noise filter:
1. Remove <form> from unconditional noise tags. ASP.NET and similar
frameworks wrap entire pages in a <form> tag — these are not input
forms. Forms with >500 chars of text are now treated as content
wrappers, not noise.
2. Add safety valve for class/ID noise matching. When malformed HTML
leaves a noise container unclosed (e.g., <div class="header"> missing
its </div>), the HTML5 parser makes all subsequent siblings into
children of that container. A header/nav/footer with >5000 chars of
text is almost certainly a broken wrapper absorbing real content —
exempt it from noise filtering.
