fix(promocode): correct activation UX, error mapping and validity dates

Map promocode errors by stable backend code (detail.code) instead of brittle English
substring matching, so previously-unmapped codes (active_discount_exists, daily_limit,
no_subscription_for_days, trial_*, etc.) show the right message instead of 'server error';
added the missing keys to all 4 locales.

valid_until now anchors to end-of-day in the admin's LOCAL timezone on both create AND
edit read-back, so codes no longer expire at the start of the day and editing no longer
drifts the date forward for negative-offset admins.

Allow 0-hour discount ('until first purchase'). Route user-facing discount deactivation
to the endpoint that rolls back promocode usage when the discount came from a promocode,
and parse the structured {code,message} error.

src/locales/en.json

@@ -787,6 +787,13 @@
         "not_yet_valid": "Promo code is not yet active",
         "used": "Promo code has already been used",
         "already_used_by_user": "You have already used this promo code",
+        "active_discount_exists": "You already have an active discount. Deactivate it first.",
+        "no_subscription_for_days": "This promo code requires an active or expired subscription",
+        "subscription_not_found": "Subscription not found",
+        "not_first_purchase": "This promo code is only available for your first purchase",
+        "daily_limit": "Too many promo code activations today",
+        "trial_subscription_exists": "You already have a subscription, so this trial code can't be applied",
+        "trial_provisioning_failed": "Couldn't provision the trial right now, please try again later",
         "user_not_found": "User not found",
         "server_error": "Server error"
       },

src/locales/fa.json

@@ -674,6 +674,13 @@
         "not_yet_valid": "کد تخفیف هنوز فعال نشده",
         "used": "کد تخفیف قبلاً استفاده شده",
         "already_used_by_user": "شما قبلاً از این کد استفاده کرده‌اید",
+        "active_discount_exists": "شما در حال حاضر یک تخفیف فعال دارید. ابتدا آن را غیرفعال کنید.",
+        "no_subscription_for_days": "این کد تخفیف به اشتراک فعال یا منقضی‌شده نیاز دارد",
+        "subscription_not_found": "اشتراک یافت نشد",
+        "not_first_purchase": "این کد تخفیف فقط برای اولین خرید در دسترس است",
+        "daily_limit": "تعداد فعال‌سازی کد تخفیف امروز بیش از حد است",
+        "trial_subscription_exists": "شما در حال حاضر اشتراک دارید، بنابراین این کد آزمایشی قابل اعمال نیست",
+        "trial_provisioning_failed": "در حال حاضر امکان فعال‌سازی نسخه آزمایشی نیست، لطفاً بعداً تلاش کنید",
         "user_not_found": "کاربر یافت نشد",
         "server_error": "خطای سرور"
       },

src/locales/ru.json

@@ -816,6 +816,13 @@
         "not_yet_valid": "Промокод ещё не начал действовать",
         "used": "Промокод уже использован",
         "already_used_by_user": "Вы уже использовали этот промокод",
+        "active_discount_exists": "У вас уже есть активная скидка. Сначала отключите её.",
+        "no_subscription_for_days": "Для этого промокода нужна активная или истёкшая подписка",
+        "subscription_not_found": "Подписка не найдена",
+        "not_first_purchase": "Промокод доступен только для первой покупки",
+        "daily_limit": "Слишком много активаций промокодов за сегодня",
+        "trial_subscription_exists": "У вас уже есть подписка, поэтому триал-промокод применить нельзя",
+        "trial_provisioning_failed": "Не удалось выдать триал прямо сейчас, попробуйте позже",
         "user_not_found": "Пользователь не найден",
         "server_error": "Ошибка сервера"
       },

src/locales/zh.json

@@ -674,6 +674,13 @@
         "not_yet_valid": "优惠码尚未生效",
         "used": "优惠码已被使用",
         "already_used_by_user": "您已使用过此优惠码",
+        "active_discount_exists": "您已有一个生效中的折扣，请先停用它。",
+        "no_subscription_for_days": "此优惠码需要有效或已过期的订阅",
+        "subscription_not_found": "未找到订阅",
+        "not_first_purchase": "此优惠码仅限首次购买使用",
+        "daily_limit": "今日优惠码激活次数过多",
+        "trial_subscription_exists": "您已有订阅，因此无法使用此试用优惠码",
+        "trial_provisioning_failed": "暂时无法开通试用，请稍后再试",
         "user_not_found": "用户不存在",
         "server_error": "服务器错误"
       },