Support multiple simultaneous Cockpit tabs

Currently multiple Cockpit tabs open at the same time conflict and cause the interface to spazz out, making it unusable.

It is already working fine to load Cockpit in separate browser instances (e.g. separate Chrome profiles, or one in incognito, or one on a different device), but they also don't share views (so it's necessary to export from one and import to the other to see the same view(s) - #418 will help with that).

It would be nice if a user with multiple monitors could just open Cockpit in two tabs and have e.g. a first person control view on one tab and move the other tab to the other window and show a map view on it.

The issue does not identify files, tests, or an entry point, so begin by locating the Cockpit UI behavior that causes simultaneous tabs to conflict. Done means two tabs can remain usable at once, display different views, and support the described multi-monitor workflow.

Written by the indexing model from the issue text.