GEOINT Flugverkehr: Kein Flackern, stabiler

- Atomarer Layer-Swap statt clearLayers (Marker verschwinden nie)
- Einzelner API-Call (radius=250nm) statt 4 Grid-Calls (weniger Rate-Limits)
- Refresh-Interval 15s -> 30s (weniger API-Last)
- moveend-Debounce 1.2s -> 2s (ruhigeres Verhalten beim Navigieren)
- Backend Cache-TTL 10s -> 20s, Koordinaten auf 0.5-Grad-Raster gerundet

src/routers/geoint.py

@@ -45,8 +45,8 @@ async def get_flights(
     _user: dict = Depends(get_current_user),
 ):
     """Proxy fuer airplanes.live API. 10s Cache, max 300 Aircraft."""
-    cache_key = f"flights:{round(lat, 1)}:{round(lon, 1)}:{radius}"
-    cached = _get_cached(cache_key, ttl=10)
+    cache_key = f"flights:{round(lat*2)/2:.1f}:{round(lon*2)/2:.1f}:{radius}"
+    cached = _get_cached(cache_key, ttl=20)
     if cached:
         return cached