ZEVA 2 - Fix date formatting in Excel export to match credit application template

**Describe the task**
This request came from the Business Area, as they mentioned that suppliers often run into formatting issues when copying the sales date from the Excel export into a new credit application template. It’s a frequent and frustrating issue for them.
After receiving this feedback, I tested the flow and was able to reproduce the problem:
1. Go to Credit Transactions
2. Open Credit Applications
3. Filter by status: Issued
4. Open any application
5. Click Download Errors
In the downloaded Excel file, the sales date looks like a normal date, but it’s not actually recognized by Excel as one. So when a supplier copies it into the credit application template and uploads it, they get a formatting error. The root of the issue is that the date format in the export isn’t valid for the template.

**Purpose**
To make sure the sales date in the Excel export uses a consistent and correct format (YYYY-MM-DD), so suppliers can copy and paste it into the template without triggering any errors.

**Acceptance Criteria**
- [ ] Sales dates in the Excel export are formatted as YYYY-MM-DD
- [ ] Pasting the date into the credit application template does not result in a formatting error

**Additional context**
We discussed this at the Inception Meeting, and I’ll add a [link](https://bcgov.sharepoint.com/:x:/r/teams/00598-TeamZelda/Shared%20Documents/Team%20Zelda/_ZEVA/ZEVA%20Rebuild/UX%20Research%20%26%20Guidelines/User%20Requests%20Log.xlsx?d=w1de1c5cb635f4b92964302c5e1d1e223&csf=1&web=1&e=0QxJly) - (row 50 )the original request as well as screenshots showing the error message that appears during upload.

Start from the Credit Transactions flow: Credit Applications, status Issued, an application, and Download Errors. Inspect where the Excel export creates the sales-date value and verify the downloaded date is recognized as YYYY-MM-DD and can be pasted into the credit application template without a formatting error.

Written by the indexing model from the issue text.