Important

Adds feature to apply discount codes to active subscriptions via settings menu, with UI and backend support.

• Behavior:
  • Adds BillingDiscountCodeButton component for entering discount codes in BillingDiscountView.
  • New mutation applyPromotionCode in cloudBillingRouter.ts to handle promotion code application.
  • Updates BillingService in stripeBillingService.ts to apply promotion codes to active subscriptions.
• UI Components:
  • BillingDiscountCodeButton.tsx: Button and dialog for entering promotion codes.
  • BillingDiscountView.tsx: Integrates BillingDiscountCodeButton to allow code entry when no discounts are present.
• Backend:
  • cloudBillingRouter.ts: Adds applyPromotionCode mutation for applying discount codes.
  • stripeBillingService.ts: Implements applyPromotionCode method to interact with Stripe API.
• Utilities:
  • Adds subscription.update.discounts.add to IdempotencyKind in stripeIdempotencyKey.ts.

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