Various changes/improvements

Fix: workaround jump mode styling issue (awaiting upcoming Textual fix).
Fix: collection tree wouldn't be refocused if jump mode was dismissed.
Add: extra bindings - ctrl+P in a TextArea opens pager, ctrl+E opens editor. This is in addition to the existing f3 and f4 bindings.
Add: warning toast if user attempts to open pager/editor but none are configured in the environment.
Add: error toast if the user attempts to open pager/editor, but it fails to run due to an OSError.

darrenburns / posting