The phone app onboards you properly and signs in to portals

Three fixes from first-day use of the phone app. On first launch against your local mesh the app now opens into an onboarding dialog — enter your name and a line about yourself, and it creates your device user with that profile, instead of silently creating an empty one that greeted you with "set up your profile". Picking a remote portal now always opens that portal's own sign-in when you have no valid session — the app never connects anonymously any more, which used to render as a blank portal. And the chat composer now follows dark mode instead of staying light.