Align shape library SVG colors with design token palette

[GeneralJerel]

Priority: P3 | Source: PR #21 self-review (F7)

Problem

Several SVG shapes in svg-shape-library.txt use hardcoded color values (#444, #ddd, #bbb, #999) that don't match the design token palette documented in svg-diagram-skill.txt (#F1EFE8, #5F5E5A, etc.).

The usage notes say "adapt colors" but the examples should lead by example.

Suggested Fix

Update the hardcoded grays in the sedan, wheel, and gear shapes to use the documented palette colors.