feat(gift): transferable gift claim — buyer share link + recipient claim page

Pairs with the bot's unified claimable-gift model. A landing gift now lands on
the buyer's success page as PAID/claimable (deferred) instead of being delivered
to a phantom recipient, so the buyer gets a transferable link to forward and the
recipient claims it themselves — guaranteeing delivery regardless of channel or
whether they pre-exist.

- api/landings.ts: PurchaseStatus gains is_claimable/claim_url/bot_claim_link;
  add GiftClaimResult + getGiftClaim()/claimGift().
- PurchaseSuccess.tsx: GiftLinkShareState — buyer sees the claim link + Telegram
  link + copy-message when a gift is PAID/claimable; stop polling for that state
  (it stays PAID until claimed) instead of spinning forever.
- GiftClaim.tsx (new) + /buy/gift/:token route: public recipient claim page with
  a Telegram arm (GIFT_ deep link) and a web/email arm (binds + one-click login),
  polling while the payment settles, idempotent "already claimed" + 404 states.
- i18n: landing.giftClaim.* / landing.giftLink.* in ru/en/zh/fa.

src/locales/zh.json

@@ -4493,6 +4493,34 @@
     "merging": "合并中..."
   },
   "landing": {
+    "giftClaim": {
+      "title": "您收到一份礼物！",
+      "error": "无法激活礼物。",
+      "notFoundTitle": "未找到礼物",
+      "notFoundDesc": "此礼物链接无效或已不可用。",
+      "alreadyTitle": "礼物已激活",
+      "alreadyDesc": "此礼物已被领取。",
+      "successTitle": "礼物已激活！",
+      "connectDesc": "使用此链接连接：",
+      "copyLink": "复制链接",
+      "pendingTitle": "即将完成…",
+      "pendingDesc": "付款仍在确认中。本页面将自动更新。",
+      "replaceWarning": "您已有订阅——激活此礼物将替换它。",
+      "activateTelegram": "在 Telegram 中激活",
+      "activateWeb": "通过邮箱激活",
+      "emailLabel": "您的邮箱",
+      "claimNow": "领取礼物"
+    },
+    "giftLink": {
+      "shareText": "我送您一份订阅！在此激活：",
+      "viaTelegram": "Telegram：",
+      "title": "礼物已就绪！",
+      "subtitle": "将此链接发送给您想赠送的人——他们自行激活。",
+      "linkLabel": "礼物链接",
+      "telegramLabel": "Telegram 链接",
+      "alsoSent": "我们也已发送到 {{contact}}。",
+      "copyMessage": "复制消息"
+    },
     "notFound": "页面未找到",
     "forMe": "为自己",
     "asGift": "作为礼物",