fix(weather): show correct wind speed and unit for imperial units

When OPENWEATHER_UNITS=imperial, OpenWeatherMap returns wind speed in
mph directly — the server was incorrectly multiplying by 3.6 (m/s→km/h)
on top of that. All locale strings also hardcoded the unit label instead
of using a {{windUnit}} placeholder, so the label always read km/h.

Resolves #79

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/locales/sv.json

@@ -65,7 +65,7 @@
     "weatherRefresh": "Uppdatera vädret",
     "weatherRefreshTitle": "Uppdatera",
     "weatherUpdated": "Väder uppdaterat",
-    "weatherFeelsLike": "Känns som {{temp}}° · {{humidity}}% · Vind {{wind}} km/h",
+    "weatherFeelsLike": "Känns som {{temp}}° · {{humidity}}% · Vind {{wind}} {{windUnit}}",
     "fabTaskLabel": "Lägg till uppgift",
     "fabCalendarLabel": "Lägg till händelse",
     "fabShoppingLabel": "Lägg till shopping",