i18n: fix missing keys and translate all non-admin frontend strings

- Add 12 missing i18n keys (t() was returning the literal key string) to
  all 13 locales: dashboard.topbar.premiumAccess,
  dashboard.translate.complete.toastOkDesc,
  dashboard.translate.progress.{connectionLost,processingFallback},
  glossaries.card.{term,created}, glossaries.termEditor.{addTerm,maxReached},
  login.google.{connecting,errorFailed,errorGeneric}, login.orContinueWith
- Add 6 FR-drift keys (landing.pricing.{free,enterprise}.{name,desc,cta})
- Add ~120 new i18n keys covering site header/footer, file-uploader,
  checkout success, dashboard pages, translate page, provider selector
  themes, language selector, translation complete, api-keys, services,
  settings, pricing (~1800 new key/locale pairs)
- Wrap hardcoded French/English in components with t() calls
- Convert LLM_THEMES/CLASSIC_THEMES/FALLBACK_PROVIDERS maps from
  hardcoded constants to t()-driven factories
- Admin pages intentionally left untouched per request

Files: 15 components/pages + src/lib/i18n.tsx
Typecheck: passes (tsc --noEmit exit 0)

frontend/src/app/dashboard/translate/TranslationComplete.tsx

@@ -111,7 +111,7 @@ export function TranslationComplete({
             : t('dashboard.translate.complete.descGeneric')}
         </p>
         <div className="mt-3 inline-flex items-center gap-1.5 rounded-full border border-emerald-200 bg-emerald-50 px-3 py-1 text-xs font-semibold text-emerald-700 dark:border-emerald-800/50 dark:bg-emerald-950/30 dark:text-emerald-400">
-          <TrendingUp className="size-3" /> Haute qualité
+          <TrendingUp className="size-3" /> {t('translateComplete.highQuality')}
         </div>
       </div>
 
@@ -122,17 +122,17 @@ export function TranslationComplete({
           <div className="flex flex-col items-center gap-1 rounded-xl border border-emerald-100 bg-emerald-50/50 p-3 dark:border-emerald-900/30 dark:bg-emerald-950/10">
             <FileText className="size-4 text-emerald-600" />
             <p className="text-sm font-bold text-foreground">142</p>
-            <p className="text-[10px] uppercase tracking-wider text-muted-foreground font-medium">Segments</p>
+            <p className="text-[10px] uppercase tracking-wider text-muted-foreground font-medium">{t('translateComplete.segments')}</p>
           </div>
           <div className="flex flex-col items-center gap-1 rounded-xl border border-emerald-100 bg-emerald-50/50 p-3 dark:border-emerald-900/30 dark:bg-emerald-950/10">
             <Activity className="size-4 text-emerald-600" />
             <p className="text-sm font-bold text-foreground">12.8k</p>
-            <p className="text-[10px] uppercase tracking-wider text-muted-foreground font-medium">Caractères</p>
+            <p className="text-[10px] uppercase tracking-wider text-muted-foreground font-medium">{t('translateComplete.characters')}</p>
           </div>
           <div className="flex flex-col items-center gap-1 rounded-xl border border-emerald-100 bg-emerald-50/50 p-3 dark:border-emerald-900/30 dark:bg-emerald-950/10">
             <Timer className="size-4 text-emerald-600" />
             <p className="text-sm font-bold text-emerald-600">96%</p>
-            <p className="text-[10px] uppercase tracking-wider text-muted-foreground font-medium">Confiance</p>
+            <p className="text-[10px] uppercase tracking-wider text-muted-foreground font-medium">{t('translateComplete.confidence')}</p>
           </div>
         </div>