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>

templates/partial-item-nav.hbs

@@ -1,10 +1,8 @@
 {{!-- Sheet Tab Navigation --}}
 <hr />
 <nav class="sheet-tabs tabs" data-group="primary">
-  <a class="item" data-tab="description">Description</a>
-  <a class="item" data-tab="details">Details</a>
-  {{#if item.effects.length}}
-  <a class="item" data-tab="effects">Effets</a>
-  {{/if}}
+  <a class="item" data-tab="description" aria-label="{{localize 'MNBL.description'}}">{{localize "MNBL.description"}}</a>
+  <a class="item" data-tab="details" aria-label="{{localize 'MNBL.details'}}">{{localize "MNBL.details"}}</a>
+  <a class="item" data-tab="effects" aria-label="{{localize 'MOURNBLADECYD2.EFFECT.activeEffects'}}">{{localize "MOURNBLADECYD2.EFFECT.activeEffects"}}</a>
 </nav>
 <hr />