Small patch for the Weather App based on reviewer feedback. Three fixes.

First, the language toggle now actually translates the full UI. Before,
switching to English left several strings in Spanish: the forecast
heading, the day labels in both the cards and the canvas chart, the
“highs / lows” legend, and most embarrassingly, the weather description
itself (“algo de nubes” instead of “scattered clouds”). The issue was
that the forecast code was hardcoded in Spanish. Now it queries the
OpenWeatherMap API with the correct lang parameter, and re-translates
the forecast cards, the canvas labels, and the legend when the language
changes.

Second, the units toggle (Celsius / Fahrenheit) was already working but
now also converts wind speed from km/h to mph when Fahrenheit is
selected, which makes sense for imperial users.

Third, the welcome state is in place. First-time visitors now see a
pulsing sun icon and a short prompt instead of a blank page with just a
search bar.

Thanks to everyone who tested and left feedback. Three reviewers asked
for multi-language support and one asked for unit conversion, so those
were the top requested features.