fix: popups no longer close on backdrop click, only via explicit close/cancel

Clicking the dimmed area outside a modal (+Task, +Invoice, expense,
review, etc.) accidentally dismissed it and lost in-progress input.
Every popup already has an explicit Cancel/Close/✕ button, so the
backdrop click handler is removed; also drops the now-dead
onClose/blockClose prop plumbing that only existed to support it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/pages/client/ClientMyInvoices.jsx

@@ -103,8 +103,6 @@ function ClientInvoiceModal({ invoice, onClose }) {
       title={invoice.invoice_number}
       subtitle={invoice.bill_to || company?.name}
       headerRight={<StatusBadge status={statusColor[invoice.status] || 'not_started'} label={`${invoiceStatusLabel(invoice.status)}${isOverdue ? ' · Overdue' : ''}`} />}
-      onClose={onClose}
-      blockClose={Boolean(downloading)}
       metaContent={<>
         <div><div style={F}>Invoice Date</div><div style={{ fontSize: 13, color: 'var(--text-primary)' }}>{invoice.invoice_date ? new Date(invoice.invoice_date).toLocaleDateString() : '—'}</div></div>
         <div><div style={F}>Due Date</div><div style={{ fontSize: 13, color: isOverdue ? 'var(--danger)' : 'var(--text-primary)' }}>{invoice.due_date ? new Date(invoice.due_date).toLocaleDateString() : '—'}</div></div>