feat(ui): add group-by-model toggle to global context menu

Adds a 'Group by Model' toggle entry to the right-click global context
menu for quick access, complementing the existing setting in
Settings → Layout Settings. The menu item shows a checkmark indicator
reflecting the current state and immediately reloads the view on toggle.

Also fixes he.json translation that was mojibake (garbled characters).

Includes:
- Context menu HTML item with check-indicator
- JS toggle logic via settingsManager
- i18n for all 10 locales
- Hebrew translation fix

locales/de.json

@@ -183,6 +183,9 @@
         },
         "manageExcludedModels": {
             "label": "Ausgeschlossene Modelle verwalten"
+        },
+        "groupByModel": {
+            "label": "Nach Modell gruppieren"
         }
     },
     "header": {