[Bug] Tabs excluded from the mixed timeline become disabled/unclickable as standalone tabs (web client)

Flare version: 1.5.1 (1510)
Platform: Web client (web.flareapp.moe), Firefox-based browser (LibreWolf) on Linux

I've got a few tabs under Home with the Mixed tab enabled. I want most of my tabs to feed into Mixed, but I have one custom Bluesky tab I'd like to keep separate; I still want to open it and read it on its own, I just don't want its posts mixed into the combined Home/Mixed feed.

The way I'd expect to do that (and the way it works in the app) is to open that tab's
settings and turn off "Show in mixed timelines." That should keep its content out of Mixed while leaving the tab itself fully usable.

On the web client though, the moment I turn off "Show in mixed timelines" for that tab, it gets greyed out in the top tab bar and I can't click into it anymore. So my only options are: (1) tab is clickable, but its posts leak into Mixed (Show in mixed timelines = on), or (2) posts stay out of Mixed, but I lose the ability to open the tab at all (off).

There's no combination that gives me "keep this tab openable AND keep it out of Mixed," which is the whole point of that toggle.

Steps to reproduce

1. Tab settings → enable "Enable mixed timeline tab."
2. Have at least two source tabs (in my case two Bluesky tabs).
3. Edit one of them and turn off "Show in mixed timelines."
4. Go back to the timeline view; that tab is now greyed out in the tab bar and can't
   be opened.

Expected: "Show in mixed timelines = off" should only exclude the tab's posts from the Mixed/Home feed. The tab should stay selectable and viewable on its own, same as in the native app.

Actual: Turning it off disables the tab entirely on web; it greys out and becomes unclickable.

I set up the identical configuration in the mobile app and it works exactly as expected there: the tab stays openable and its content stays out of Mixed at the same time. So this looks like a web-client-specific regression rather than a config mistake on my end.

Start by reproducing the configuration from Tab settings in the web client's timeline view, focusing on the top tab bar behavior when “Show in mixed timelines” is disabled. Compare the affected tab with the mobile app's behavior; done means the tab remains selectable while its posts stay excluded from the Mixed timeline.