feat(send): add pending payment UI

[pwltr]

Description

For hold invoices (or slow payments), when the send doesn’t complete in 10 seconds, show a pending screen and, when the payment later succeeds or fails, show a toast and navigate to Success or Failure.

Linked Issues/Tasks

Closes #448

Screenshot / Video

Simulator.Screen.Recording.-.iPhone.17.-.2026-02-26.at.12.43.33.mov

QA Notes

Use bitkit-docker to generate and settle/cancel hold invoices

    holdinvoice [amount] [-m memo]     Create a hold invoice
    settleinvoice <preimage>           Reveal a preimage and use it to settle the corresponding invoice
    cancelinvoice <payment_hash>       Cancels a currently open invoice