Improve article TOC, sticky header, and cross-language anchors

- Pin the site header on scroll (position: absolute -> fixed) so it no
  longer disappears when reading.
- Redesign the desktop table-of-contents sidebar: compact spacing and fix
  the first-item clipping at 100% zoom (drop fixed-height flex centering in
  the scroll container for a flex column with max-height).
- Add the article title above the desktop TOC so readers always know which
  article they are in.
- Make the article TOC a site-wide standard: main.js now auto-builds the
  sidebar + sticky mobile header from each page's own h1/h2 headings, so all
  languages (EN/SI/MK) get it with no per-page HTML. Existing hand-written
  EN labels are preserved.
- Update the URL hash to the active section while scrolling (replaceState,
  no history spam, no jump).
- Add transliteration for readable anchors in every language: Slovenian
  diacritics and Macedonian Cyrillic map to ASCII slugs.

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

css/layout/_header.css

@@ -15,7 +15,9 @@
 
 /* 1. Glavni kontejner za glavo */
 .dropdown-header-navigation {
-    position: absolute;
+    position: fixed;
+    top: 0;
+    left: 0;
     width: 100%;
     height: 80px;
     background: #FFFFFF;