🎨 Palette: Add confirmation dialog for payment deletion

[shadowcoder8]

💡 What: Added a native browser confirm() dialog to the deletePayment function in frontend/payment-management.js. It also now provides alert() feedback upon success or failure.
🎯 Why: Deleting a payment is a destructive action that previously happened immediately on button click, risking accidental data loss. This change adds a necessary friction point to prevent mistakes and aligns the payment management page with the delete behavior on other pages.
📸 Before/After: Clicking "Delete" now prompts "Are you sure you want to delete this payment?" before sending the API request.
♿ Accessibility: N/A (Standard browser interaction).

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PR created automatically by Jules for task 2906207038865582029 started by @shadowcoder8

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