Add transformation diagram and rewrite section using Werling notation

[fjp]

Summary

• Add new SVG diagram (transformation_cart_frenet.svg) illustrating the Cartesian-to-Frenet coordinate transformation
• Rewrite the Transformation section text to use Werling paper notation ($\vec{r}(s)$, $\vec{t}_r$, $\vec{n}_r$, $\vec{x}(s,d)$)
• Replaces the missing frame-components.jpg image that was reported as broken

Fixes #11
Fixes #3

Test plan

• Verify the SVG renders correctly on GitHub
• Verify the transformation equation and notation are consistent with the diagram