Add all 15 sections matching README table of contents

- Split Bonus Topics into separate sections (11-15)
- Added Section 11: Dimensionality Reduction (PCA, SVD)
- Added Section 12: Information Theory (Entropy, KL Divergence)
- Added Section 13: Support Vector Machines (Linear, Soft Margin, Kernels)
- Added Section 14: Decision Trees & Ensembles (Gini, Entropy, Bagging, Boosting)
- Added Section 15: Bias-Variance Tradeoff
- Updated navigation with all 15 section buttons
- Added more formulas from README content
- Updated hero stats to show "15 Topics"

Author: cursoragent