accounts/billing: update email verification and billing (#23112)

## Description
2 birds, one stone
- Update email address: Adds details about email verification, number of
emails per account
- Billing: Remove coupon section

## Related issues or tickets
https://docker.atlassian.net/browse/ENGDOCS-2860
https://docker.atlassian.net/browse/ENGDOCS-2853

## Reviews
- [ ] Editorial review

Author: sarahsanders-docker

content/manuals/accounts/manage-account.md

@@ -47,7 +47,20 @@ To update your email address, select **Email**:
 3. Select **Send verification email** to send a verification email to your new
 email address.
 
-Once you verify your email address, your account information will update.
+Your new email address will appear as unverified until you complete the
+verification process. You can:
+
+- Resend the verification email if needed.
+- Removed the unverified email address at any time before verification.
+
+To verify your email, open your email client and follow the instructions
+in the Docker verification email.
+
+> [!NOTE]
+>
+> Docker accounts only support one verified email address at a time, which
+is used for account notifications and security-related communications. You
+can't add multiple verified email addresses to your account.
 
 ### Change your password
 

content/manuals/billing/payment-method.md

@@ -2,7 +2,7 @@
 title: Add or update a payment method
 weight: 20
 description: Learn how to add or update a payment method in Docker Hub
-keywords: payments, billing, subscription, supported payment methods, failed payments, coupons
+keywords: payments, billing, subscription, supported payment methods, failed payments
 alisases:
     - /billing/core-billing/payment-method/
 ---
@@ -204,14 +204,3 @@ Docker also sends an email notification `Action Required - Credit Card Payment F
 
 Once the grace period is over and the invoice is still not paid, the subscription downgrades to a free subscription and all paid features are disabled.
 
-## Redeem a coupon
-
-You can redeem a coupon for any paid Docker subscription.
-
-A coupon can be used when you:
-- Sign up to a new paid subscription from a free subscription
-- Upgrade an existing paid subscription
-
-You are asked to enter your coupon code when you confirm or enter your payment method.
-
-If you use a coupon to pay for a subscription, when the coupon expires, your payment method is charged the full cost of your subscription. If you don't have a saved payment method, your account downgrades to a free subscription.