Add Download CSV Button to Holdings Page

[CameronBeneteau]

We have a button on the performance page so users can download the data in CSV format starting from the currently selected date. We should add the same functionality for the holdings page. Same button style, same location on the page. Should download the holdings data in CSV format of the current date and portfolio. Ensure naming is consistent with what the performance page does so it should include the portfolio and date. Something like holdings_data_benchmark_2025-03-24.csv.

Ref:

• https://github.com/DFIC-Quant-Fund/Fund-Monitor-Web/blob/main/src/app/performance/page.tsx#L61
• https://fund.degrootefinance.com/performance
• https://fund.degrootefinance.com/holdings