fix(subscription): recover stepper when a pending checkout is abandoned

A user who picked a plan + brands, clicked the checkout button to
create the pending subscription, then closed the tab without paying
came back to a frozen "Mevcut Plan · Bekliyor" card with no payment
button and no way to edit. Status was "pending", which my conditional
treated as an active subscription and routed away from the stepper.

Frontend
- hasActiveSub narrowed to active|cancelled only. Pending users now
  see the stepper again.
- New effect pre-fills selectedPlanKey, selectedBrandIds,
  billingPeriod from the pending row on first render and jumps
  straight to the payment step.
- New PendingPaymentBanner at the top of the stepper with
  "Odemeye devam et" (scrolls + sets step=payment) and "Vazgec"
  (calls cancel-pending then resets selection).

Backend
- subscriptions.service.create() auto-expires existing pending
  rows for the user before inserting a new one — abandoned checkouts
  no longer accumulate and a fresh attempt with a different plan
  doesn't 409.
- New PATCH /subscriptions/cancel-pending + service method for
  the banner's explicit cancel action.

i18n: subscription.pendingBanner.* (tr/en).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/messages/en.json

@@ -256,6 +256,13 @@
       "title": "Your trial is ending soon!",
       "description": "{days} days left. Upgrade now to continue accessing all features.",
       "cta": "Upgrade Plan"
+    },
+    "pendingBanner": {
+      "title": "You have a pending payment",
+      "description": "Checkout for {plan} ({brands}) was left incomplete. Resume it or cancel to pick a different plan.",
+      "resumeCta": "Resume payment",
+      "cancelCta": "Cancel",
+      "cancelled": "Pending subscription cancelled. You can pick a new plan."
     }
   },
   "payment": {

apps/web/src/messages/tr.json

@@ -256,6 +256,13 @@
       "title": "Deneme süreniz dolmak üzere!",
       "description": "{days} gününüz kaldı. Tüm özelliklere erişmeye devam etmek için hemen yükseltin.",
       "cta": "Plana Yükselt"
+    },
+    "pendingBanner": {
+      "title": "Bekleyen ödemen var",
+      "description": "{plan} planı, {brands} için ödeme yarıda kaldı. Devam edebilir veya farklı plan seçmek için vazgeçebilirsin.",
+      "resumeCta": "Ödemeye devam et",
+      "cancelCta": "Vazgeç",
+      "cancelled": "Bekleyen abonelik iptal edildi. Yeni plan seçebilirsin."
     }
   },
   "payment": {