fix(i18n): return French error messages in auth, register, download endpoints

routes/admin_routes.py

@@ -137,7 +137,7 @@ async def require_admin(authorization: Optional[str] = Header(None)) -> str:
         )
     token = parts[1]
     if not verify_admin_token(token):
-        raise HTTPException(status_code=401, detail="Invalid or expired token")
+        raise HTTPException(status_code=401, detail="Token invalide ou expiré")
     return ADMIN_USERNAME