Improve discovery of preview in kolibri for guest users

Summary

• Change UI according the following figma design.
• Implements a sidePanel for a preview of channels.
• Dynamically change icons and buttons for guest and logged-in users.

https://github.com/user-attachments/assets/aa0c5bcc-47d7-41af-ad46-5c7519058bf4

https://github.com/user-attachments/assets/5f58fba9-aee4-4fbb-9c82-12937ffd817d

References

closes #3083

Reviewer guidance

• Test all the possible permutations with demo URL and source URL set and unset.
• The Icons and side panel should match the designs attached above.