content: add real photos + captions to all Student Welcome Guide pages

Replace the "Image placeholder" boxes on all 30 guide subpages + the guide
landing hero with real, optimized photos and captions, EN/MK/SI (93 figures).

- 31 source photos (up to 18 MB) optimized to WebP (<=1400px, all <500 KB)
  as images/guide-<slug>.webp.
- Captions follow the Get-to-Know style: description + "Photo:/Фото:/Foto:"
  + linked source (or MSOS for own event photos). Photographer credits kept.
  MK/SI descriptions are translated (proofread welcome).
- CSS: move the banner crop from the figure onto the <img> so the caption
  shows below it (was clipped by the figure's fixed height + overflow).

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

en/student-welcome-guide/administrative-basics/index.html

@@ -198,8 +198,9 @@
                 <h1>Essential administrative tools</h1>
                 <p class="article-subtitle">EMŠO, a tax number, SI-PASS, a bank account, and a phone plan unlock almost every other service.</p>
             </header>
-            <figure class="guide-hero-image guide-hero-image--placeholder">
-                <span><i class="fas fa-image" aria-hidden="true"></i>Image placeholder</span>
+            <figure class="guide-hero-image">
+                <img width="1024" height="576" fetchpriority="high" decoding="async" src="../../../images/guide-administrative-basics.webp" alt="The FURS financial administration logo on a sign.">
+                <figcaption>The FURS financial administration logo on a sign. Photo: <a href="https://www.nadlani.si/novice/furs-z-nujnim-opozorilom-ne-odpirajte-laznega-sporocila-ki-krozi-v-njihovem-imenu/" target="_blank" rel="noopener">nadlani.si</a></figcaption>
             </figure>
 
             <div class="article-body">