cmux: find which window holds a tab before saying it opened

In cmux, cmux ssh-session-attach --session-id term_... returns the existing surface's ID if the terminal already has a tab. It doesn't open a new one, so a printed OK doesn't mean the user can see it. Run cmux tree --all and check the window: the tab may sit in a second app window that isn't key, or is behind or off-screen. To show it, run cmux focus-window --window <uuid from list-windows --json>, then cmux workspace select --workspace <ref> and cmux focus-panel --panel surface:<n> --workspace <ref> --window <uuid>. Point the CLI at the right app's socket with that app bundle's own bin/cmux; DEV and release builds have separate sockets.