Fix: Add missing MNBL i18n keys and show effects tab always

- Added MNBL.details and MNBL.description to lang/fr.json
- Removed conditional display of effects tab in partial-item-nav.hbs
- Effects tab now always visible in item sheets
- Added MNBL i18n keys verification to test script

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

lang/fr.json

@@ -47,6 +47,8 @@
     "chaos": "Chaos",
     "difficulty": "Difficulté",
     "duration": "Durée",
+    "details": "Détails",
+    "description": "Description",
     "elementslords": "Seigneurs des Éléments",
     "equipment": "Equipement",
     "examples": "Exemples",