Harden nested SVG transforms and viewBox handling

[mezotv]

Problem

Kiwi uses each path's screen CTM, which helps, but nested groups, transformed SVG roots, and unusual viewBox/preserveAspectRatio combinations can still produce incorrect geometry or stroke widths.

Impact

Real-world logos can import at the wrong scale, position, or stroke weight.

Suggested scope

• Build fixtures with nested g transforms, root transforms, and non-square viewBox scaling.
• Verify geometry coordinates and stroke width are emitted in rendered CSS-pixel space.
• Handle non-uniform scaling intentionally, especially for stroke width.

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Linear issue: NOT-76