refactor(baoyu-article-illustrator): extract palette as independent third dimension

- Create palettes/ directory with macaron, warm, neon palette files
- Move macaron from styles/ to palettes/ (color scheme, not rendering style)
- Extract warm palette variant from vector-illustration into shared palette
- Add neon palette extracted from retro style colors
- Update architecture from Type × Style to Type × Style × Palette
- Add Palette Gallery and override rules to styles.md
- Add Palette Override section to prompt-construction.md
- Update presets table with Palette column
- Add palette selection step to workflow
- Add preferred_palette to EXTEND.md schema

skills/baoyu-article-illustrator/references/palettes/macaron.md

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+# macaron
+
+Soft macaron pastel color blocks on warm cream
+
+## Background
+
+- Color: Warm Cream (#F5F0E8)
+- Texture: Subtle warm paper grain
+
+## Colors
+
+| Role | Color | Hex | Usage |
+|------|-------|-----|-------|
+| Background | Warm Cream | #F5F0E8 | Primary background |
+| Primary Text | Deep Charcoal | #2D2D2D | Headlines, main text, outlines |
+| Macaron Blue | Sky Blue | #A8D8EA | Info block fill, cool-toned zones |
+| Macaron Mint | Mint Green | #B5E5CF | Info block fill, growth/positive zones |
+| Macaron Lavender | Lavender | #D5C6E0 | Info block fill, abstract/concept zones |
+| Macaron Peach | Peach | #FFD5C2 | Info block fill, warm-toned zones |
+| Accent | Coral Red | #E8655A | Key data, warnings, emphasis |
+| Muted Text | Warm Gray | #6B6B6B | Secondary annotations, small labels |
+
+## Accent
+
+Coral Red (#E8655A) for key data, warnings, and emphasis highlights. Use sparingly — one or two elements per illustration.
+
+## Best For
+
+Educational content, knowledge sharing, concept explainers, tutorials, tech summaries, onboarding materials