perf: add confirmation dialogs to DeletePaymentButton and TimeEntryModal delete

[macwilling]

Problem

Two destructive actions have no confirmation step and insufficient loading feedback:

1. DeletePaymentButton (app/(admin)/invoices/[invoiceId]/DeletePaymentButton.tsx)

• A single click on a small icon button permanently deletes a payment record
• No confirmation step — easy to misclick in a dense UI
• Pending state is opacity-50 only — no label change to communicate "Deleting…"
• No window.confirm() either (it was never added) — just fires immediately

2. TimeEntryModal delete (components/time/TimeEntryModal.tsx:176)

• "Delete" button in the edit modal footer fires immediately on click
• No confirmation step before permanently deleting a time entry
• A misclick in the modal footer (Cancel / Delete are adjacent) is easy

Fix

DeletePaymentButton

Replace the bare <button> with a pattern that:

1. Shows a confirmation Dialog on first click
2. Shows "Deleting…" text while isPending
3. Disables both Cancel and Delete buttons while pending

TimeEntryModal delete

Add a confirmation step before handleDelete executes — either:

• An inline useState(false) confirmation prompt within the modal footer ("Are you sure?" + Confirm/Cancel buttons replacing the Delete button), or
• A separate small Dialog

Acceptance criteria

• DeletePaymentButton requires a confirmation step before deleting
• DeletePaymentButton shows a text label change while deleting (not just opacity)
• TimeEntryModal delete requires a confirmation step
• Both confirmations are non-blocking (Dialog, not window.confirm())
• npm run build passes