fix: round €/m² in Telegram, drop "Bilder nachladen" admin button, fix lightbox visibility

- notifications: round sqm_price to whole € in Telegram match messages
  (was emitting raw float like "12.345614 €/m²").

- wohnungen: remove the admin-only "Bilder nachladen (N)" button. It
  flickered into view whenever a freshly-scraped flat was still in
  pending state, which was effectively random from the user's point of
  view, and the manual backfill it triggered isn't needed anymore — new
  flats are auto-enriched at scrape time. Also drops the dead helpers
  it was the sole caller of: enrichment.kick_backfill,
  enrichment._backfill_runner, db.flats_needing_enrichment,
  db.enrichment_counts.

- lightbox: the modal didn't appear because Tailwind's Play CDN injects
  its own .hidden { display: none } rule at runtime, which kept fighting
  our class toggle. Switch the show/hide to inline style.display so no
  external stylesheet can mask it. Single-class .lightbox now only owns
  the layout — the initial-hidden state is on the element via
  style="display:none".

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

web/static/app.css

@@ -138,9 +138,8 @@ body:has(#v_map:checked) .view-map { display: block; }
    image. Prev arrow is hidden on the first image; next arrow on the last. */
 .lightbox { position: fixed; inset: 0; z-index: 1000;
             background: rgba(8, 18, 32, .92);
-            display: flex; align-items: center; justify-content: center;
+            align-items: center; justify-content: center;
             animation: lightbox-fade .15s ease-out; }
-.lightbox.hidden { display: none; }
 .lightbox-image { max-width: 92vw; max-height: 88vh; object-fit: contain;
                   border-radius: 8px; box-shadow: 0 10px 40px rgba(0,0,0,.5);
                   background: #0c1726; }