content(mss-2026): add sponsor logo + event banners, update venue to NLB branch

- Add Capital Asset Management sponsor logo (images/partners/capital.png),
  replacing the plain-text sponsor name in the event partners row.
- Set the in-article hero to the clean event banner (mss-2026-hero.webp) and
  the News/homepage listing cards to the sponsor-strip promo variant
  (mss-2026-card.webp) via a new front-matter `card:` field.
- Update the venue everywhere (event page key info + prose + confirmation
  text, and the homepage promo banner) to
  "НЛБ експозитура, локација East Gate Mall, Скопје" (EN: NLB branch;
  SI: poslovalnica NLB), across all three languages.

Build tooling: build_content emits an optional data-card on the hero <img>;
build_listings prefers data-card as the listing thumbnail so the card can
differ from the in-article hero. Rebuilt news pages, listings and search index.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

si/news/index.html

@@ -207,7 +207,7 @@
 <!-- AUTO-NEWS:START -->
                 <article class="newshub-card" data-type="news">
                     <a class="newshub-media" href="/si/news/meet-student-slovenia-2026/">
-                        <img width="1920" height="1280" src="/images/event4-img-1.webp" alt="Študenti in govorci na dogodku „Spoznaj študentsko Slovenijo“ v Skopju" loading="lazy">
+                        <img width="1920" height="1080" src="/images/mss-2026-card.webp" alt="Promocijski plakat „Spoznaj študentsko Slovenijo 2026“ — poslovalnica NLB, East Gate Mall, Skopje, 4. september 2026" loading="lazy">
                         <span class="news-badge news-badge--news"><i class="fas fa-bullhorn" aria-hidden="true"></i> Novica</span>
                     </a>
                     <div class="newshub-body">