feat: add an account dashboard for managing saved invoices

[Navdeepannu]

Depends on: feat: add authentication and secure account-scoped invoice persistence

Goal

Replace the current device-local saved-invoice experience with a signed-in dashboard where users can find, continue, duplicate, download, and manage their invoices.

Scope

• Account-scoped invoice list.
• Search by invoice number, client, or company.
• Filter by draft, sent, paid, overdue, and archived status.
• Sort by created date, updated date, due date, or total.
• Continue editing an invoice.
• Duplicate an invoice without reusing its identifier.
• Delete or archive an invoice with confirmation.
• Download PDF/image from the dashboard.
• Pagination or cursor-based loading.
• Loading, empty, error, and no-results states.

Data displayed per invoice

• Invoice number.
• Client name.
• Company name.
• Issue and due dates.
• Total and currency.
• Status.
• Last updated time.