This PR updates the README with several improvements:
- Added a light/dark mode compatible logo using the `<picture>` element
- Added a tagline: "Your AI second brain for saving and organizing everything that matters"
- Added badges for Web App, Chrome Extension, and Raycast Extension
- Added a developer resources section with links to the Developer Console and Documentation
- Added detailed sections for the Browser Extension and Raycast Extension features
- Fixed minor typos and grammar issues
- Updated all screenshots with newer versions
- Added a new logo-light-fullmark.svg file for light mode display
- Removed the "Quick Start for Contributors" section as it's covered in the [CONTRIBUTING.md](http://CONTRIBUTING.md)
