A mic tap opened capture, and with it the OS permission prompt, before
anything asked the host whether it could transcribe; the setup sheet only
appeared after the host refused dictation.start. The session screen now
gates the start on the setup read it already does, opens the setup sheet
when setup is missing, and hands the next tap back to the host and re-reads
when the sheet closes. A host that never had a model selected now offers
the mic. The sheet's switch uses MobileSwitch.
Fixes#35203