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/templates/_wohnungen_body.html

@@ -97,7 +97,26 @@
 </section>
 
 <!-- Karte (Leaflet-Container bleibt über HTMX-Swaps hinweg erhalten) -->
-<section class="view-map">
+<section class="view-map space-y-2">
+    <div class="card p-3 text-xs text-slate-600 flex items-center justify-between gap-3 flex-wrap">
+        <div>
+            {{ map_matched_with_coords }} / {{ map_matched_total }} passende Wohnungen mit Koordinaten
+            {% if map_matched_without_coords %}
+            · <span class="chip chip-warn">{{ map_matched_without_coords }} ohne Koordinaten</span>
+            {% endif %}
+        </div>
+        {% if is_admin and map_matched_without_coords %}
+        <form method="post" action="/actions/backfill-coords"
+              hx-post="/actions/backfill-coords" hx-target="#wohnungen-body" hx-swap="outerHTML">
+            <input type="hidden" name="csrf" value="{{ csrf }}">
+            <button class="btn btn-ghost text-xs" type="submit"
+                    {% if not gmaps_available %}disabled title="GMAPS_API_KEY fehlt"{% endif %}
+                    hx-confirm="Fehlende Koordinaten jetzt über Google Maps nachladen?">
+                Koordinaten nachladen
+            </button>
+        </form>
+        {% endif %}
+    </div>
     <div class="card p-3">
         <div id="flats-map" hx-preserve="true"></div>
     </div>