map view (Leaflet + OSM), iOS switches, Alarm → Benachrichtigungen

* flats: new lat/lng columns (migration v3); alert geocodes every new flat
  through googlemaps and ships coords in the payload
* web: CSP extended for unpkg (leaflet.css) + tile.openstreetmap.org
* Wohnungen tab: Liste/Karte view toggle (segmented, CSS-only via :has(),
  selection persisted in localStorage). Karte shows passende flats as Pins
  on an OSM tile map; Popup per Pin mit Adresse, Zimmer/m²/€ und Link
* Top-strip toggles are now proper iOS-style toggle switches (single
  rounded knob sliding in a pill, red when on), no descriptive subtitle
* Alarm-Karte verlinkt jetzt auf /einstellungen/benachrichtigungen
  (Filter-Karte bleibt /einstellungen/filter)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

alert/maps.py

@@ -23,6 +23,20 @@ class Maps:
     def __init__(self):
         self.gmaps = googlemaps.Client(key=GMAPS_API_KEY)
 
+    def geocode(self, address):
+        """Return (lat, lng) or None for a Berlin address string."""
+        if not address:
+            return None
+        try:
+            res = self.gmaps.geocode(f"{address}, Berlin, Germany")
+            if not res:
+                return None
+            loc = res[0]["geometry"]["location"]
+            return (float(loc["lat"]), float(loc["lng"]))
+        except Exception as e:
+            logger.warning("geocode failed for %r: %s", address, e)
+            return None
+
     def _get_next_weekday(self, date, weekday):
         days_ahead = weekday - date.weekday()
         if days_ahead <= 0: