Remove repeated text while parsing html

[sauravpanda]

Currently, in some HTML files, texts are repeated as mobile and nonmobile content is repeated. We should remove this to reduce noise.

[sauravpanda]

Fixed in #302. Added removeHiddenAndDuplicateElements() to HTMLCleaner — removes aria-hidden=true, inline display:none/visibility:hidden, and responsive CSS class heuristics (mobile-only, desktop-hidden, etc.) before text extraction. Called in clean(), cleanSemantic(), and preserveSemanticHierarchy().