docs: add SVG version of logo

[johnsoncodehk]

Adds logo.svg, a vector redraw of logo.png (rounded-square icon, cyan-to-indigo layered waves, glowing white "TS").

How it was drawn:

• Waves: 9 smooth Bézier wave layers stacked on a base gradient. Their edges follow the actual wave boundaries of the PNG, which were extracted as edge ridges and spline-smoothed. Each layer has one linearGradient, with colors solved by least squares against the PNG. A soft highlight runs along the lighter side of each edge, mimicking the ribbon look of the original.
• Letters: geometric shapes fitted to the PNG's letter mask (IoU 0.95): T is two rounded rects, S is a round-capped stroked curve. Shading uses an edge color plus a blurred, masked bright core, with an outer halo.
• Filters use color-interpolation-filters="sRGB" to avoid banding in the dark areas.

The size is 11 KB, versus 412 KB for the PNG. Chrome and resvg render it nearly identically. logo.png and README.md are unchanged.

Left: original PNG, right: SVG rendered in Chrome

PNG vs SVG

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