Turning link editing off now applies to connected visitors instantly

When you switch your project's shared link from "can edit" to view-only, everyone who already has the project open now loses edit access within a second - their editor switches to a read-only state with a clear notice. Turning editing back on unlocks connected visitors just as instantly.

Previously the toggle only applied to people who opened the link *after* the change: visitors who were already connected could keep typing until they reloaded the page, which made the setting look broken.