feat(ui): green map pin for applied flats, hide map reject after apply, lightbox image viewer

Map: replace Leaflet's default marker with a divIcon SVG pin coloured
per state — green when the user has already successfully applied
(status.chip === "ok"), brand-blue otherwise. Same condition also hides
the action buttons in the popup, matching the list view, which already
hid both Bewerben and Ablehnen on success — so the only remaining
action on an applied flat is opening the original ad link.

Image gallery: clicks now open a global lightbox modal instead of a new
tab. The viewer fits each image into the viewport via max-width/height
+ object-fit: contain (uniform sizing regardless of source aspect),
shows × top-right, prev/next arrows on the sides, ←/→/Esc keyboard
nav, and click-on-backdrop to close. Prev arrow is hidden on the first
image and next on the last. Tile changes from <a target="_blank"> to
<button> since the new-tab fallback is no longer wanted.

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

web/templates/_wohnung_detail.html

@@ -10,9 +10,9 @@
 <div class="px-4 py-4 space-y-3">
     <div class="flat-gallery">
         {% for src in image_urls %}
-        <a class="flat-gallery-tile" href="{{ src }}" target="_blank" rel="noopener">
+        <button type="button" class="flat-gallery-tile" data-full-src="{{ src }}" aria-label="Foto {{ loop.index }} öffnen">
             <img src="{{ src }}" loading="lazy" alt="Foto {{ loop.index }}">
-        </a>
+        </button>
         {% endfor %}
     </div>
     <div class="text-xs">