[Enhancement] - add refund feature in transaction history screen

[islandbitcoin]

for all locally saved transaction history items, add a refund button that returns the same amount of the transaction back to the sender.

we can use lnurl-withdraw to complete the refund

[islandbitcoin]

Refer to BTCPay Server integration in flash-pos for rewards points.
We are using LNURL-w from the btcpayserver endpoint to give rewards.

Please use the same method to create refund LNURL-w codes.

[patoo0x]

📋 Definition of Done — 💰 75,000 sats

Expected Behavior After Fix:

• Each transaction in the history screen has a "Refund" button
• Tapping Refund initiates an LNURL-withdraw flow returning the exact transaction amount to the original sender
• Refund completes successfully and the refunded transaction is visually marked in history
• Refund button is disabled or hidden for transactions that have already been refunded
• Error states handled gracefully (sender unreachable, expired invoice, insufficient balance)

Deliverables:

• PR against main referencing this issue (closes #46)
• Unit tests for the refund flow (success, already-refunded, error cases)
• Screen recording showing: initiate refund → LNURL-withdraw completes → history updated
• Lightning address provided in your first comment on this issue

Review Gate:

• All existing tests pass
• Nick signs off
• Dread final approval

Payment: 75,000 sats via Lightning on merge.
See CONTRIBUTING.md for full details.