fix: replace hardcoded French strings with i18n keys in SynthesisDetail

Replace "Lire la suite" and "Reduire" with t('synthesis.readMore')
and t('synthesis.collapse'). Adds both keys to fr.ts.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/i18n/fr.ts

@@ -97,6 +97,8 @@ const fr = {
   'synthesis.title': 'Synthese de la Semaine {week}',
   'synthesis.generatedAt': 'Generee le {date}',
   'synthesis.backLink': 'Retour aux syntheses',
+  'synthesis.readMore': 'Lire la suite',
+  'synthesis.collapse': 'Reduire',
   'synthesis.delete': 'Supprimer',
   'synthesis.deleteConfirmMessage':
     'Etes-vous sur de vouloir supprimer cette synthese definitivement ?',

frontend/src/pages/SynthesisDetail.tsx

@@ -34,6 +34,7 @@ function truncateSummary(text: string, level: number): string {
 
 /** Renders a single news article with its title (linked) and summary. */
 const NewsItemCard: Component<{ item: NewsItemType; displayLevel: number }> = (props) => {
+  const { t } = useI18n();
   const [expanded, setExpanded] = createSignal(false);
 
   const effectiveLevel = () => expanded() ? 4 : props.displayLevel;
@@ -71,7 +72,7 @@ const NewsItemCard: Component<{ item: NewsItemType; displayLevel: number }> = (p
           onClick={() => setExpanded(true)}
           class="mt-2 text-xs text-indigo-600 hover:text-indigo-800 font-medium"
         >
-          Lire la suite &darr;
+          {t('synthesis.readMore')} &darr;
         </button>
       </Show>
       <Show when={expanded() && props.displayLevel < 4}>
@@ -79,7 +80,7 @@ const NewsItemCard: Component<{ item: NewsItemType; displayLevel: number }> = (p
           onClick={() => setExpanded(false)}
           class="mt-2 text-xs text-indigo-600 hover:text-indigo-800 font-medium"
         >
-          Reduire &uarr;
+          {t('synthesis.collapse')} &uarr;
         </button>
       </Show>
     </div>