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/pricing/page.tsx

@@ -464,7 +464,7 @@ export default function PricingPage() {
               href={isLoggedIn ? "/dashboard" : "/"}
               className="px-6 py-2 rounded-full text-[9px] font-black uppercase tracking-widest text-foreground/40 hover:text-foreground transition-all"
             >
-              Dashboard
+              {t('pricing.dashboard')}
             </Link>
             {isLoggedIn && (
               <Link
@@ -486,7 +486,7 @@ export default function PricingPage() {
             ? "bg-emerald-50 border-emerald-200 text-emerald-700 dark:bg-emerald-950/50 dark:border-emerald-800 dark:text-emerald-300"
             : "bg-red-50 border-red-200 text-red-700 dark:bg-red-950/50 dark:border-red-800 dark:text-red-300"
         )}>
-          <span className="text-lg">{toastMsg.type === 'ok' ? '✓' : '✕'}</span>
+          <span className="text-lg">{toastMsg.type === 'ok' ? t('pricing.okSymbol') : t('pricing.errSymbol')}</span>
           <p className="text-sm flex-1">{toastMsg.text}</p>
           <button onClick={() => setToastMsg(null)} className="text-muted-foreground hover:text-foreground text-lg leading-none">&times;</button>
         </div>