Switch to SVG logo for better scaling

**Better Icon Quality: Use logo.svg instead of logo.png**

**Changes:**
- Copied logo.svg to extension directory
- Updated package.json to use logo.svg for sidebar icon
- SVG provides better scaling at different sizes and themes

**Benefits:**
- **Crisp at all sizes** - Vector graphics scale perfectly
- **Theme adaptable** - SVG can adapt to light/dark themes
- **Smaller file size** - More efficient than PNG for simple graphics

Author: nikomatsakis