localization: add Greek translation (#2416)

Add complete Greek (el_GR) localization with all 998 keys translated.
Register the locale in App.axaml and Models/Locales.cs, and update
TRANSLATION.md via the localization-check script.

Author: teras

TRANSLATION.md

@@ -87,6 +87,8 @@ This document shows the translation status of each locale file in the repository
 
 </details>
 
+### ![el__GR](https://img.shields.io/badge/el__GR-%E2%88%9A-brightgreen)
+
 ### ![es__ES](https://img.shields.io/badge/es__ES-%E2%88%9A-brightgreen)
 
 ### ![fr__FR](https://img.shields.io/badge/fr__FR-98.90%25-yellow)

src/App.axaml

@@ -12,6 +12,7 @@
       </ResourceDictionary.MergedDictionaries>
 
       <ResourceInclude x:Key="de_DE" Source="/Resources/Locales/de_DE.axaml"/>
+      <ResourceInclude x:Key="el_GR" Source="/Resources/Locales/el_GR.axaml"/>
       <ResourceInclude x:Key="en_US" Source="/Resources/Locales/en_US.axaml"/>
       <ResourceInclude x:Key="fr_FR" Source="/Resources/Locales/fr_FR.axaml"/>
       <ResourceInclude x:Key="he_IL" Source="/Resources/Locales/he_IL.axaml"/>

src/Models/Locales.cs

@@ -9,6 +9,7 @@ public class Locale
 
         public static readonly List<Locale> Supported = new List<Locale>() {
             new Locale("Deutsch", "de_DE"),
+            new Locale("Ελληνικά", "el_GR"),
             new Locale("English", "en_US"),
             new Locale("Español", "es_ES"),
             new Locale("Français", "fr_FR"),