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/profile/page.tsx

@@ -207,7 +207,7 @@ export default function ProfilePage() {
           )}>
             {statusMsg.type === 'ok' ? <CheckCircle2 className="w-4 h-4 shrink-0 mt-0.5" /> : <XCircle className="w-4 h-4 shrink-0 mt-0.5" />}
             <span className="flex-1">{statusMsg.text}</span>
-            <button onClick={() => setStatusMsg(null)} className="text-muted-foreground hover:text-foreground">✕</button>
+            <button onClick={() => setStatusMsg(null)} className="text-muted-foreground hover:text-foreground" aria-label="Close">✕</button>
           </div>
         )}