Design a dark mode color palette

**Description:**
Design a dark theme alternative to the current purple gradient.

**Requirements:**
- High contrast (WCAG AA compliant, contrast ratio >4.5:1)
- Works well for LinkedIn/Twitter dark mode
- Maintain professional indie hacker aesthetic
- 5-6 colors: background, panel_bg, primary, secondary, text, accent

**Todo:**
- [ ] Design color palette (provide hex codes)
- [ ] Create mockup or color swatch image
- [ ] (Optional) Update `agents/layout_compositor.py` colors dict
- [ ] Add example output showing dark theme

**Good for:** Designers (no coding required! Just submit hex codes in a comment)

**Current colors (for reference):**
```python
colors = {
'background': '#f8f9fa',
'panel_bg': '#ffffff',
'primary': '#667eea',
'secondary': '#764ba2',
'text': '#1a202c',
'accent': '#43e97b',
}
```

**Resources:**
- Color contrast checker: https://webaim.org/resources/contrastchecker/
- Dark theme inspiration: https://www.happyhues.co/