Make weather update interval configurable, was hardcoded to 30 min

Screen.poll_interval was a fixed class attribute the scheduler read
directly -- added Screen.get_poll_interval(settings) so a screen can make
it settings-driven instead. WeatherScreen overrides it to read a new
"update_minutes" field (default 30, matching the old hardcoded value).
New number input on the Weather settings page.

Caught a real edge case while testing: `raw or 30` treats an explicit 0
as falsy and silently replaces it with 30 instead of clamping to the
1-minute floor. Not reachable via the UI (min="1" on the input) but the
method should still be correct standalone -- fixed with an explicit
None-check instead.

screens/base.py

@@ -26,3 +26,9 @@ class Screen(ABC):
         """Settings this screen needs, with defaults, merged under config.json's
         settings[self.id] on first run."""
         return {}
+
+    def get_poll_interval(self, settings: dict) -> int:
+        """Seconds between check() calls. Override to make it configurable
+        via settings (e.g. a user-facing "update every N minutes" field);
+        defaults to the fixed class-level poll_interval."""
+        return self.poll_interval

screens/weather.py

@@ -22,10 +22,21 @@ WEEKDAY_ABBR_DE = ["Mo", "Di", "Mi", "Do", "Fr", "Sa", "So"]
 class WeatherScreen(Screen):
     id = "weather"
     display_name = "Weather"
-    poll_interval = 1800  # 30 minutes -- weather doesn't need to be fresher
+    poll_interval = 1800  # fallback default (30 min) if settings has no update_minutes yet
 
     def default_settings(self) -> dict:
-        return {"city": "", "latitude": None, "longitude": None, "forecast_days": 3}
+        return {"city": "", "latitude": None, "longitude": None, "forecast_days": 3, "update_minutes": 30}
+
+    def get_poll_interval(self, settings: dict) -> int:
+        raw = settings.get("update_minutes")
+        try:
+            # `raw or 30` would also catch a legitimate 0 (falsy) and silently
+            # replace it with 30 instead of clamping to the 1-minute floor
+            # below -- only fall back to the default when it's genuinely unset.
+            minutes = int(raw) if raw is not None else 30
+        except (TypeError, ValueError):
+            minutes = 30
+        return max(1, minutes) * 60
 
     def geocode(self, city: str):
         """Resolve a city name to coordinates via Open-Meteo's free geocoding