feat: add private payment requests

[ben-kaufman]

This PR adds private Paykit Payment Requests to Bitkit.

Description

1. Automatically opens incoming requests in the existing Send confirmation flow with the requesting contact, exact amount, and a Payment Request title.
2. Keeps dismissed requests actionable through a bell, preview sheet, and full request history, with manual reopen and explicit rejection.
3. Adds outgoing request creation from Receive for linked, saved contacts, including amount, note, expiry, queued delivery state, and sent history.
4. Drops expired or remotely unavailable requests, keeps presentation state scoped to the active Pubky identity, and protects account changes and overlapping actions.
5. Requires strict private resolution for requests: a consumed Private Payment List is never reused, another endpoint from that list is not attempted, and public details are never used as fallback while waiting for a newer list.
6. Updates Paykit to 0.1.0-rc44 and adds local E2E homeserver configuration plus safe cold-start restoration for externally managed Pubky sessions.

The request payload itself remains SDK-backed and durable; Bitkit persists only identity-scoped presentation suppression, not a duplicate request queue. Payment proofs and receipts remain out of scope.

Dependencies:

• Paykit 0.1.0-rc44
• Local Locks interoperability was verified with paykit-server#2 at 41cda2567226a690a012770017d5e7c1d49e2a2b.
• Companion Android PR: synonymdev/bitkit-android#1172

Linked Issues/Tasks

N/A

Screenshot / Video

N/A — proof recordings were completed locally and are intentionally not attached to the PR.

QA Notes

Manual Tests

• 1. Clean wallet → create Pubky profile → enable Paykit and Contact Payments → add the peer as a contact: private-capable request action appears once the Noise link is established.
• 2. Peer creates a private request → Home: Payment Request opens automatically with the correct contact and amount.
• 3. Payment Request → dismiss without rejecting → bell → request preview → Pay: the request remains queued, reopens, and pays successfully.
• 4. Peer creates a second request after payment → Pay: a newer Private Payment List is used; the consumed list is not reused and no public fallback occurs.
• 5. Receive → Send Payment Request → enter amount, note, and expiry → select linked contact → Send: request is queued once and appears in sent history.
• 6. Incoming request → Reject: only that request becomes terminal and the private payment list is not consumed.
• 7. Incoming request → dismiss → relaunch: request remains discoverable without automatically reopening again; expired requests disappear live.
• 8. Cross-platform E2E: Android creates two requests that iOS receives and pays, and iOS creates two requests that Android receives and pays, on clean regtest state.

Automated Checks

• BitkitTests/PaykitPaymentRequestServiceTests.swift: 46 tests cover mapping, eligibility, proposal delivery, rejection, expiry, identity isolation, presentation races, queue durability, fresh-list retry, and action reconciliation.
• BitkitTests/PaykitSdkClientConfigTests.swift: 4 tests cover production/local configuration and safe deferred session restoration.
• Focused test run: 50 tests passed on the iOS simulator.
• SwiftFormat lint passed for all 20 changed Swift files.
• Translation validation passed with 0 errors.
• Both final cross-platform proof videos decoded end to end without errors.

[ovitrif]

Approved. Choose Recipient keeps an in-sheet back control next to the timer, so users can return from that pushed page.