Prefer handwritten font

Use the Google Fonts API to fetch a handwritten font, which gives the app a
modicum of personality. There are more "best practices" ways to do this, such
as:

- Download the font once, and include it in the bundle
- Extend the Tailwind configure to recognize the font
- Ditch the inline <style> block

But I don't need the performance benefits that the first bullet provides. And
the second two bullets are more relevant for a larger application with more than
one font. So I think in this case, the easiest solution is best.

Also:
- Use `container` and `mx-auto` to constrain content for wide screens

scratch/habit-screens/client/src/Habits.elm

@@ -146,7 +146,7 @@ render { today, visibleDayOfWeek, completed } =
 
         Just weekday ->
             div
-                [ class "font-sans py-6 px-6"
+                [ class "container mx-auto py-6 px-6"
                 , tailwind [ ( "pt-20", today /= visibleDayOfWeek ) ]
                 ]
                 [ header []