feat(i18n): add Azerbaijani (az 🇦🇿) language support

- Add az locale to config/i18n.json (source of truth, 42 locales total)
- Create src/i18n/messages/az.json (UI strings from en.json base)
- Create docs/i18n/az/ directory with full documentation set
- Add 🇦🇿 Azərbaycan dili to README.md language bar
- Add az entry to docs/i18n/README.md index (40 doc languages)
- Add az to generate-multilang.mjs LOCALE_SPECS (Google TL: az)
- Add az to i18n_autotranslate.py lang_map
- Update CHANGELOG.md with feat(i18n) entry

config/i18n.json

@@ -13,6 +13,14 @@
       "english": "Arabic",
       "flag": "🇸🇦"
     },
+    {
+      "code": "az",
+      "label": "AZ",
+      "name": "Azərbaycan dili",
+      "native": "Azərbaycan dili",
+      "english": "Azerbaijani",
+      "flag": "🇦🇿"
+    },
     {
       "code": "bg",
       "label": "BG",