Add artifact-based vectorizer comparison examples

[swernerx]

Goal

Add artifact-based comparison examples against common vectorization approaches, starting with one small case where Morphēa, Potrace, and at least one manual/hosted baseline can be discussed fairly.

Why this matters

The README now explains how Morphēa differs from Illustrator Image Trace, Vectorizer.AI, and Potrace. The next step is proof: small, inspectable examples showing where the output differs in editability, node count, primitive type, grouping, and cleanup effort.

Proposed first example

Start with a synthetic or safely licensed logo/icon-like image:

• simple enough to inspect by eye;
• contains a circle or stroke that classic tracing may fragment;
• has a clear expected editable SVG structure;
• can be included in a public docs/gallery page.

Acceptance criteria

• Add a docs page or gallery entry with side-by-side artifacts: input bitmap, Morphēa output, and at least one external tracing baseline where licensing/terms allow publication.
• Compare concrete metrics: primitive count, node/parameter count, layer/group structure, and visual error if available.
• Keep the comparison factual. Say where the other tool is better if it is.
• Link the example from docs/vectorizer-comparison.md once available.

Notes

Do not publish outputs from hosted/commercial tools unless their terms allow it. Potrace is the easiest first baseline because it is local and scriptable.