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, sheet transitions, 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 encrypted, 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 iOS PR: synonymdev/bitkit-ios#676

Preview

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: iOS creates two requests that Android receives and pays, and Android creates two requests that iOS receives and pays, on clean regtest state.

Automated Checks

• PaykitPaymentRequestRepoTest.kt: covers mapping, eligibility, proposal delivery, rejection, expiry, identity-scoped presentation state, and action serialization.
• PaykitSdkServiceTest.kt: covers exact identity enforcement and safe deferred session restoration.
• AppViewModelSendFlowTest.kt: covers automatic/manual presentation, sheet transitions, identity changes, newer-list retry, strict private resolution, and payment lifecycle races.
• PaymentRequestExpirationTest.kt: covers expiry selection and retained draft state.
• SheetHostTest.kt: covers locked sheet dismissal and scrim input isolation during durable proposal creation.
• Local verification passed: app compile, Android-test compile, complete dev unit suite, detekt, and git diff --check.
• Both final cross-platform proof videos decoded end to end without errors.

[ovitrif]

Looks good. Durably queued requests stay confirmed after an identity change, and a consumed private payment list is never reused or replaced by public details.

[ovitrif]

Local Locks interoperability was verified with pubky/paykit-server#2 at 41cda2567226a690a012770017d5e7c1d49e2a2b.

Note this paykit-server needs to integrated into the bitkit-docker and e2e tests soonish 🙏🏻

cc. @jvsena42 @piotr-iohk

[piotr-iohk]

Local Locks interoperability was verified with pubky/paykit-server#2 at 41cda2567226a690a012770017d5e7c1d49e2a2b.

Note this paykit-server needs to integrated into the bitkit-docker and e2e tests soonish 🙏🏻

cc. @jvsena42 @piotr-iohk

As far as paykit-server it would be good to have a staging deployment since paykit e2e tests are run against our staging regtest and also using staging homeserver (as far as I understand that was the plan, see: #1084 (comment))

Server staging
The intended next server-side QA step is to deploy Paykit Server on staging once its runtime/listener composition is implemented. There is no staging endpoint yet, and that work is outside these mobile PRs.

[ovitrif]

Navigating back from Payment Request sheet should return you to Payment Requests (list) screen. It instead shows the Receive Bitcoin QR, with Payment Requests still behind the sheet.

[jvsena42]

Review of the payment request flows. just compile and just test pass; the ComposeUi instrumented lane was run on a Pixel 9 AVD and all 15 new tests pass (after 864f008 fixed CreatePaymentRequestScreenTest querying a merged-semantics node). The 8 other failures in that lane reproduce on master and are unrelated.

Findings inline, roughly most-severe first. The SheetHost dismissEnabled work looks sound to me: programmatic hide() bypasses confirmValueChange, the disabled scrim sits under the sheet, and the inner NavHost BackHandlers still take priority over the swallowed sheet back handler.

[ovitrif]

The QR no longer sits under Request Payment, but in-sheet back still does not return to Payment Requests because that screen still only calls popBackStack().

[ovitrif]

List-driven Request Payment now starts on the form, and in-sheet back closes the sheet so you return to Payment Requests.