design-systems: add 74 brand DESIGN.md files (VoltAgent/awesome-design-md)

- 74 brands: airbnb, stripe, apple, figma, linear, vercel, etc.
- 147 files: DESIGN.md + README.md per brand (~2.1 MB)
- Each DESIGN.md contains structured brand analysis (colors, typography, components)
- Updated 00-overview.md with new design-systems directory

concepts/design-principles.md

@@ -0,0 +1,37 @@
+---
+title: Design Principles for Conversion
+description: Core design principles that drive conversions on premium landing pages.
+tags: [design, conversion, psychology, principles]
+---
+
+# Design Principles for Conversion
+
+## 1. Visual Hierarchy
+- Size = importance (H1 > H2 > Body > Caption)
+- Color = action (CTA buttons should be most contrasting)
+- Whitespace = focus (isolate key elements)
+
+## 2. Fitt's Law
+- Make CTAs large and easily clickable
+- Place important actions within thumb reach on mobile
+- Use 48x48px minimum touch targets
+
+## 3. Hick's Law
+- Simplify choices on first view
+- Progressive disclosure: show more on interaction
+- Limit CTA buttons to 1-2 per section
+
+## 4. Weber-Fechner Law
+- Gradual changes feel natural
+- Animations should be smooth (ease-in-out)
+- Incremental reveal builds anticipation
+
+## 5. Von Restorff Effect
+- Stand-out elements are remembered
+- Use accent color for primary CTA
+- Unique visual treatment for key metrics
+
+## Anti-Patterns
+- Don't use accent color for everything
+- Don't make all headings the same size
+- Don't cram content — respect whitespace