docs: Update marketplace URL format to full GitHub URL

- Update plugin marketplace add command from 'daymade/claude-code-skills' to full GitHub URL
- Add marketplace name clarification (daymade-skills from marketplace.json)
- Update all plugin install commands to use @daymade-skills suffix
- Standardize marketplace references across all documentation files
- Update installation scripts to use new URL format

Affected files:
- CLAUDE.md: Development commands and skill creation workflow
- CONTRIBUTING.md: Contribution guidelines
- QUICKSTART.md: Quick start guide
- QUICKSTART.zh-CN.md: Chinese quick start guide
- README.md: Main documentation
- README.zh-CN.md: Chinese documentation
- demos/index.html: Demo page
- scripts/install.ps1: Windows installation script
- scripts/install.sh: Unix installation script

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

CONTRIBUTING.md

@@ -89,10 +89,11 @@ Before submitting, validate your skill:
 5. **Test locally:**
    ```bash
    # Add your fork as marketplace
-   /plugin marketplace add your-username/claude-code-skills
+   /plugin marketplace add https://github.com/your-username/claude-code-skills
+   # Marketplace name comes from .claude-plugin/marketplace.json
 
    # Install and test
-   /plugin install productivity-skills
+   /plugin install productivity-skills@your-marketplace-name
    ```
 
 6. **Submit Pull Request:**