Valve, being stupid as shit as usual, decided it'd be a fucking WONDERFUL idea to blanket-ban the "changeteam" command across all servers, unless they're official competitive, so it was possible to get stuck in spectator, unable to join the game, and also unable to swap teams.

I've took it upon myself to fix this. It's now possible to switch teams by typing !changeteam in chat. If you type that and it still doesn't put you into the game from spectator, just use the change class button and pick a class, it'll put you in after that.