Header customer search and invoice reference search in admin

Admins working multiple tickets at once asked for a faster way to jump between customers and invoices without backing out to the dashboard. We added the global header search and a focused invoice-reference search.

• Added a header customer search alongside the organization member and organization detail search.
• Added an InvoiceSearch component for searching invoices by their reference ID directly from the invoice tab.
• Enhanced the invoice component with billing-email display and a one-click copy action.
• Added the default payment card on the invoice detail so admins can confirm which card the charge attempted.