Set up PROD Account in Worldline

#### Description:

Set up a payment account in Wordline for PRDT Production environment.

Once PROD is in a more polished state, the PCI team will require a review where the PCI auditor will perform a test transaction, do a source code review, etc.

#### Acceptance Criteria:

Given I'm a visitor
When I go through the checkout in PROD
Then I can successfully complete a transaction

#### Development Checklist:

- [ ] Set up the production secrets for `MERCHANT_ID`, `HASH_KEY`, and `WORLDLINE_WEBHOOK_SECRET` in GitHub Environment Settings
- [ ] Update `deploy-api-prod` accordingly
- [ ] Set up the approved and declined Transaction Response Pages in Worldline
- [ ] Set up the Response Notification - Payment Gateway with `WORLDLINE_WEBHOOK_SECRET` in Wordline
- [ ] Able to make a purchase in PROD with a real credit card.

#### Dependencies

- #101

**Relevant documentation as reference**

**Definition of Ready**

- [ ] Acceptance criteria are included
- [ ] Wireframes are included (if applicable)
- [ ] Design / Solution is accepted by Product Owner (if applicable)
- [ ] Dependencies are identified (technical, business, regulatory/policy)
- [ ] Story has been estimated (under 13 pts)

**Definition of Done**
- In progress:
- [ ] Acceptance criteria are tested (Functionality meets the acceptance criteria defined in the ticket)
- [ ] UI meets accessibility requirements
- [ ] Unit tests are written
- [ ] Work is traceable in GitHub
- [ ] PR linked to ticket number
- [ ] If needed/required - Dev adds flag/label to highlight any migration steps necessary prior to PROD deployment
- Code review:
- [ ] Code is peer reviewed and has passed CI/CD tests
- QA:
- [ ] Acceptance criteria are tested (Functionality meets the acceptance criteria defined in the ticket)
- [ ] Code is potentially shippable to the production environment
- [ ] Functional features have been tested and passed by QA
- [ ] UI components tested by designer
- [ ] Code is deployed to PROD when moved to 'done' column (unless requested otherwise by PO)
- PO Review:
- [ ] Acceptance criteria are tested (Functionality meets the acceptance criteria defined in the ticket)
- [ ] Reviewed and approved by Product Owner

#### Notes:
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Start by checking dependency #101, the GitHub Environment Settings, and the deploy-api-prod configuration. Then review the Worldline setup for transaction response pages and webhook notifications. Done means a real PROD checkout completes successfully and the PCI-related production setup is ready for review.

Written by the indexing model from the issue text.