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/templates/_wohnungen_body.html

@@ -84,17 +84,6 @@
         <span class="sep">·</span>
         <span>aktualisiert <span class="countdown" data-counter-up-utc="{{ last_scrape_utc }}">…</span></span>
         {% endif %}
-        {% if is_admin and (enrichment_counts.pending or enrichment_counts.failed) %}
-        <span class="sep">·</span>
-        <form method="post" action="/actions/enrich-all"
-              hx-post="/actions/enrich-all" hx-target="#wohnungen-body" hx-swap="outerHTML">
-            <input type="hidden" name="csrf" value="{{ csrf }}">
-            <button class="btn btn-ghost text-xs" type="submit"
-                    hx-confirm="Bilder für ausstehende Wohnungen nachladen? Kann einige Minuten dauern.">
-                Bilder nachladen ({{ enrichment_counts.pending + enrichment_counts.failed }})
-            </button>
-        </form>
-        {% endif %}
         <div class="view-toggle ml-2">
             <label>
                 <input type="radio" name="view_mode" id="v_list" value="list" checked>