docs: replace email addresses with GitHub issue links

- Remove all @example.com email addresses from documentation
- Replace security@example.com with GitHub security issue links
- Replace conduct@example.com with GitHub issue link
- Update CONTRIBUTING.md to use GitHub issues instead of email
- Ensure all communication happens through GitHub's issue tracking system
- Avoid direct email communication for better transparency and tracking

README.md

@@ -138,7 +138,7 @@ PicPeak takes security seriously:
 - 📝 Activity logging
 - 🔒 Secure file access
 
-Found a security issue? Please email security@example.com
+Found a security issue? Please open a [security issue](https://github.com/the-luap/picpeak/issues/new?labels=security) on GitHub
 
 ## 📸 Screenshots