Convert tumpang tindih sentence similarity to pure Jaccard Index, removing all TF-IDF and Cosine dependencies from overlap calculation

Update main overlap_score calculation to use pure Jaccard Index of stopword-filtered keyword sets

Implement Jaccard index stopword and conjunction filtering in compute_overlap function

Clean up project structure: delete model_lexical.py and remove all its references/fallbacks, move compute_overlap to preprocessor.py, and remove TEKS COCOK badge from sidebar, retaining only sentence snippet previews

upload ke HF