map debug + coord backfill, remove email channel, countdown label

- Surface "X/Y passende Wohnungen mit Koordinaten" on the Karte view +
  admin-only "Koordinaten nachladen" button (POST /actions/backfill-coords)
  that geocodes missing flats via Google Maps directly from the web container
- Add googlemaps dep + GMAPS_API_KEY env to web service
- Light console.log in map.js ("rendering N/M markers", "building Leaflet…")
  so the browser DevTools shows what's happening
- Drop e-mail channel from notifications UI, notify dispatcher, and _alert_status;
  coerce legacy 'email' channel rows back to 'ui' on save
- Countdown said "Aktualisierung läuft…" next to "nächste Aktualisierung" →
  shortened to "aktualisiere…"

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

web/static/map.js

@@ -39,6 +39,8 @@ function renderMarkers(data) {
   const fp = fingerprintOf(data);
   if (fp === currentFingerprint) return;
   currentFingerprint = fp;
+  const geo = data.filter((f) => typeof f.lat === "number" && typeof f.lng === "number").length;
+  console.log(`[lazyflat.map] rendering ${geo}/${data.length} markers`);
 
   if (markerLayer) {
     markerLayer.clearLayers();
@@ -70,6 +72,7 @@ function renderMarkers(data) {
 }
 
 function buildMap(el) {
+  console.log(`[lazyflat.map] building Leaflet instance (container ${el.clientWidth}×${el.clientHeight})`);
   mapInstance = L.map(el, {
     zoomControl: false,
     scrollWheelZoom: false,