Add Gallery page (per-event albums + lightbox); remove video-thumbnail blur

- New multilingual Gallery page (en/mk/si) with 9 event albums and a
  keyboard-accessible lightbox (prev/next scoped per album)
- Reuses existing event photos; links each album to its event post
- New css/pages/_gallery.css + setupGallery() lightbox in main.js
- "Gallery" link added to the "What We Do" nav (desktop + mobile) site-wide
- Gallery URLs added to sitemap.xml with hreflang
- Landing "Every Student Has a Story": removed backdrop blur on the video
  thumbnail, kept the bluish gradient tint

Note: images/original/ (458 MB of raw source photos, gitignored + unused by
the site) moved out of the working tree to reclaim disk.

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

si/support/index.html

@@ -82,6 +82,7 @@
                         <a href="#">Kaj delamo</a>
                         <ul class="dropdown-menu">
                             <li><a href="../../si/projects/">Dogodki in projekti</a></li>
+                            <li><a href="../../si/gallery/">Galerija</a></li>
                             <li><a href="../../si/blog/">Blog</a></li>
                         </ul>
                     </li>
@@ -140,6 +141,7 @@
                 <a href="#">Kaj delamo</a>
                 <ul class="dropdown-menu">
                     <li><a href="../../si/projects/">Dogodki in projekti</a></li>
+                    <li><a href="../../si/gallery/">Galerija</a></li>
                     <li><a href="../../si/blog/">Blog</a></li>
                 </ul>
             </li>