tweak: broaden enable-export message since it applies to QT too

[adil192]

The enable-export message is no longer specific to GNOME/gtk.

I tweaked the description to make it slightly friendlier for a non-technical user:

• "Apply current theme to GNOME and KDE non-COSMIC apps"
  Someone new to Linux who chose Pop!_OS might know what COSMIC is, but not what GNOME or KDE are.
• "Not all toolkits apps support auto-switching."
  I don't think the average user knows what a toolkit is.
• "may need to be restarted closed and reopened"
  To avoid conflating this with a system restart.

Related:

• feat: add color schemes for qt apps libcosmic#1121
• feat: apply qt themes alongside gtk themes cosmic-settings-daemon#128

For reviewer:

• Decide if you like the above tweaks or not.
• I've left the non-English translations alone. Do I need to delete them for them to show up in Weblate again?
• I think it's okay to merge this PR before feat: apply qt themes alongside gtk themes cosmic-settings-daemon#128 since I'm not making an explicit reference to QT.

PR checklist:

• I have disclosed use of any AI generated code in my commit messages.
  • If you are using an LLM, and do not fully understand the changes it is making to the code base, do not create a PR.
  • In our experience, AI generated code often results in overly complex code that lacks enough context for a proper fix or feature inclusion. This results in considerably longer code reviews. Due to this, AI authored or partially authored PRs may be closed without comment.
• I understand these changes in full and will be able to respond to review comments.
• My change is accurately described in the commit message.
• My contribution is tested and working as described.
• I have read the Developer Certificate of Origin and certify my contribution under its conditions.

[mmstick]

We need to get the feature merged in the settings daemon first