fix: use core LNURL-pay validation

[ovitrif]

Description

This PR:

1. Updates the app from Android release v2.3.0 to bitkit-core 0.1.74.
2. Routes LNURL-pay invoice fetching through core with full LnurlPayData.
3. Removes app-local LNURL-pay invoice callback fetching while leaving withdraw/channel behavior unchanged.
4. Maps core invoice validation errors to a neutral payment-canceled message and adds repository coverage.

Patch commit: a960a3499cc38535a2c57803272e694b5c296503
Core release: https://github.com/synonymdev/bitkit-core/releases/tag/v0.1.74

Refs:

• fix: validate LNURL-pay amount bitkit-core#115
• fix: use core LNURL-pay validation bitkit-ios#607

Preview

N/A

QA Notes

Manual Tests

• 1. Send -> scan LNURL-pay request -> complete payment: invoice fetch and send behavior match the requested payment.
• 2. regression: Send -> scan LNURL-withdraw or LNURL-channel request: existing withdraw/channel behavior still works.

Automated Checks

• Unit tests added: LightningRepoTest covers core delegation and validation-error handling.
• Local verification: just test.
• Runtime proof: Android and iOS before/after LNURL-pay validation recordings completed locally.

[ovitrif]

added a few nits that must be addressed. PR changes should be squashed into a single commit with same message as PR name

[ovitrif]

added a few nits that must be addressed. PR changes should be squashed into a single commit with same message as PR name

Addressed the review nits in the attached threads and squashed the branch into a single commit named fix: use core LNURL-pay validation.

Resolved in a960a34

[piotr-iohk]

LGTM. Manual test on staging regtest: normal LN + QuickPay on/off OK. CI @lnurl_1 green - sufficient regression for the LNURL-pay validation hotfix.