Landscape orientation, redesigned web UI, rotation on/off + minutes, weather by city name

- Panel is mounted sideways: render landscape (600x400), rotate to the
  panel's native portrait orientation right before writing to hardware.
- Web UI: card-based layout, dark mode, active nav highlighting, save
  confirmation toasts, error banners.
- Rotation: separate enabled/disabled toggle (off pins to the first screen
  in the list) and the interval is now in minutes instead of raw seconds.
  Migrates existing config.json from the old interval_seconds field.
- Weather: type a city name instead of hunting down coordinates, resolved
  via Open-Meteo's free geocoding API. Manual lat/long still available as
  a fallback.

screens/weather.py

@@ -11,6 +11,7 @@ from screens.render_utils import load_font, text_width
 logger = logging.getLogger(__name__)
 
 HTTP_TIMEOUT = 10
+GEOCODE_URL = "https://geocoding-api.open-meteo.com/v1/search"
 
 # WMO weather codes -> (German description, symbol). Not exhaustive, covers
 # the common cases; unmapped codes fall back to a generic description.
@@ -47,7 +48,29 @@ class WeatherScreen(Screen):
     poll_interval = 1800  # 30 minutes -- weather doesn't need to be fresher
 
     def default_settings(self) -> dict:
-        return {"latitude": None, "longitude": None}
+        return {"city": "", "latitude": None, "longitude": None}
+
+    def geocode(self, city: str):
+        """Resolve a city name to coordinates via Open-Meteo's free geocoding
+        API (no key needed). Returns {"latitude", "longitude", "label"} or
+        None if nothing matched."""
+        response = requests.get(
+            GEOCODE_URL,
+            params={"name": city, "count": 1, "language": "de"},
+            timeout=HTTP_TIMEOUT,
+        )
+        response.raise_for_status()
+        results = response.json().get("results") or []
+        if not results:
+            return None
+
+        top = results[0]
+        label_parts = [top.get("name"), top.get("admin1"), top.get("country")]
+        return {
+            "latitude": top["latitude"],
+            "longitude": top["longitude"],
+            "label": ", ".join(p for p in label_parts if p),
+        }
 
     def check(self, settings: dict):
         lat = settings.get("latitude")