FTUE: Ensure the right panel is disabled until explicitly triggered for new users

[nadonomy]

• The right panel is distracting for new users, so should be disabled until triggered by the user
• As a general rule, the right panel should only display when a button in the top right is explicitly clicked (maybe related)

[Cadair]

Also maybe related #10149 ? As you wouldn't want to enable it on one tab and have it switch to another unexpectedly.

[turt2live]

While I'm here, here's a list of issues to fix:

• Collapsing the right sidebar scrolls to the bottom in a room #9822
• The right-pane keeps re-opening itself on window resize #8772
• Right panel unexpectedly switches to member list when changing rooms #10149
• this one