Improve UX for enabling Wayland data control protocol in Clipboard Manager

[nalladev]

Currently, when opening the COSMIC clipboard manager applet, users are shown a
message explaining that the Wayland ext-data-control-v1 protocol is required,
along with a shell command they must manually run and then restart their session.

While the security reasoning makes sense, this flow is difficult and
intimidating for many users:

• It requires using the terminal
• It requires understanding environment variables and session restarts
• There is no explicit consent UI, only instructions

This could be improved with a more user-friendly, explicit consent flow.

Possible improvements:

• A button like “Enable Clipboard History” or “Allow Clipboard Access”
• A dialog explaining the security implications in simple terms
• On confirmation, automatically writing the required environment variable
  in a user-scoped config (instead of asking the user to run a command)
• Prompting the user to log out / restart the session to apply changes

This would be similar to how mobile platforms handle sensitive permissions:
explicit user consent, clear explanation, and no manual commands required.

The goal is not to weaken security, but to make opting in to clipboard history
clear, intentional, and accessible to non-technical users.