feat: redesign the weather overlay and add a temperature curve

[lucasclgibson]

Keeps the four condition photographs and redesigns everything on top of them.

• Removes <app-header>; the date line and brand logo are now plain markup fed by SDK helpers
• Temperature becomes the hero (18rem landscape, 14rem portrait); glass cards and backdrop blurs are gone, replaced by a legibility scrim
• Adds a smoothed temperature curve with six-hourly clock marks, a dotted "now" rule and high/low readings
• Portrait stacks the curve under the temperature at full width
• Long city names step down a size, with an ellipsis backstop, verified at all ten resolutions
• Background is now set by class instead of body.style.backgroundImage; error and forecast visibility likewise

Bundle drops from 5.67 MB to 4.50 MB despite keeping the photographs, since the removed component graph outweighed them.

Note: the curve is forward-looking only. Showing the elapsed part of the day needs historical hours, which OpenWeatherMap puts behind One Call 3.0.

[vpetersson]

screenshots/no-api-key-2160x3840.webp

This should be an impossible state for a few reasons:

1. We should serve cached data if we have data from the last few hours if the API is unreachable
2. If we have no cached data (or if is too old), we should never emit ready_signal, and subsequently the page will never show. Later on, we can move this to abort_signal when that is released.