Demo tweaks

[rkistner]

These are some minor tweaks to the supabase-todolist demo app, fixing issues that I ran into when testing.

1. Set the correct keyboard type for all password fields. Without this, the input was hidden, but the keyboard would use auto-correct for example, and wouldn't integrate with password managers. This prevented me from signing in.
2. Add scrolling to sign-in and sign-up screens. A sign-in error could move content off-screen, which made it unusable after an error.
3. Use enableEdgeToEdge() to avoid the system bar having the same color as the background. I don't fully understand all the options and implications here, but this appeared to be the simplest and most consistent solution.

[simolus3]

Thanks 👍