feat: support incoming paykit requests

[ben-kaufman]

Description

This PR builds on #630 to support incoming Paykit payment requests:

• Updates Paykit to 0.1.0-rc39 and uses its separate public and private payment resolution APIs.
• Receives supported one-time Bitcoin payment requests while Bitkit is active, discarding expired or unsupported requests.
• Reuses the existing send confirmation and payment flow, with a Payment Request title, fixed requested amount, and requesting contact.
• Accepts a request only after the user approves it, before submitting the payment.
• Uses public payment details only when no Noise channel is established and never falls back from private to public resolution.
• Persists consumed private payment-list versions before submission, treats submitted, pending, and uncertain payments as consumed, waits for newer details, and serializes private payments per contact and receiver path.
• Advertises payment-request support with the live Paykit session.

Payment proofs and receipts remain out of scope.

Linked Issues/Tasks

• Base PR: feat: add Paykit server accounts #630
• Companion Android PR: feat: support incoming paykit requests bitkit-android#1098

Screenshot / Video

N/A — the existing payment UI is reused, and no media is attached.

QA Notes

Manual Tests

• 1. Receive a request from a linked Paykit contact while Bitkit is active: the Payment Request confirmation opens with the contact and requested amount.
• 2. Swipe to pay: the request is accepted and payment continues through the existing send flow.
• 3. Receive or retain a request past its expiration: it is discarded and not presented.
• 4. Attempt another private payment before the contact publishes a newer payment list: Bitkit waits and does not reuse the consumed details or fall back to public details.

Automated Checks

• PaykitPaymentRequestServiceTests.swift: request mapping, expiry, lifecycle, acceptance, and refresh concurrency.
• PrivatePaykitServiceTests.swift: consumed-list persistence and prevention of private payment-detail reuse.
• PublicPaykitServiceTests.swift: separate public payment endpoint parsing and resolution.
• 40 selected Paykit tests passed in the iOS simulator.
• SwiftFormat, translation validation, and git diff --check passed.

[greptile-apps]

Greptile Summary

This PR adds support for receiving and paying incoming Paykit requests. The main changes are:

• Polling, filtering, and presenting incoming one-time Bitcoin requests.
• Private and public payment resolution through the Paykit rc39 APIs.
• Persistent tracking of consumed private payment-list versions.
• Request acceptance through the existing send confirmation flow.
• Payment-request capability advertising and localized UI text.

Confidence Score: 4/5

The backup migration and payment submission paths need fixes before merging.

• Existing Paykit backups fail against the new JSON wrapper.
• LNURL fetch failures leave requests accepted and private details consumed without a payment attempt.
• Amount-bearing invoices can submit a different amount from the one shown for approval.

PrivatePaykitService+Backup.swift, LnurlPayConfirm.swift, and SendConfirmationView.swift

Security Review

An amount-bearing Bolt11 endpoint is submitted using its embedded amount without checking that it matches the Paykit request amount shown to the user. A stale or malformed private endpoint can therefore change the amount that is paid.

Important Files Changed

Filename	Overview
Bitkit/Services/PaykitPaymentRequestService.swift	Adds request parsing, synchronization, expiration handling, presentation deduplication, and acceptance state.
Bitkit/Services/PrivatePaykitService+Payments.swift	Adds private request resolution, public fallback rules, and consumed-version enforcement.
Bitkit/Services/PrivatePaykitService+Backup.swift	Wraps Paykit backup state in a new JSON shape without restoring the previous raw-string format.
Bitkit/Views/Wallets/Send/LnurlPayConfirm.swift	Accepts and consumes incoming requests before the LNURL invoice is fetched.
Bitkit/Views/Wallets/Send/SendConfirmationView.swift	Integrates request acceptance and consumption but can submit an embedded invoice amount that differs from the requested amount.
Bitkit/AppScene.swift	Adds active-scene polling and serialized request presentation through the send sheet.
Bitkit/Services/PubkyService.swift	Adapts the Paykit integration to separate public and private rc39 APIs and advertises request support.

Sequence Diagram

sequenceDiagram
    participant Peer as Paykit Peer
    participant Manager as Request Manager
    participant Resolver as Private Resolver
    participant UI as Send Confirmation
    participant Wallet

    Peer->>Manager: Proposed payment request
    Manager->>Resolver: Resolve endpoint for requested amount
    Resolver-->>UI: Payment target and list version
    UI->>Manager: Accept request
    UI->>Resolver: Persist consumed version
    UI->>Wallet: Fetch invoice and submit payment
    Note over UI,Wallet: LNURL fetch currently happens after acceptance and consumption

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