feat: add Paykit subscriptions

[ben-kaufman]

Description

Adds the payer side of Paykit subscriptions, stacked on #683.

• Receives private subscription proposals and lets the payer review and confirm them.
• Requires an immediately due first period to be paid before showing the subscribed success state; failed or uncertain payments remain due and can be retried.
• Turns each unpaid billing period into the existing incoming payment-request flow, including automatic presentation, the bell queue, and the Payments tab.
• Schedules local due-payment notifications and opens the corresponding request when the notification is selected.
• Adds the Figma-aligned Subscriptions and Payments tabs, subscription detail/status views, cancellation, empty states, and fixed/open-ended summaries.
• Associates payment proofs with their exact billing period so recurring periods remain independent while retaining private-only resolution and fresh Private Payment List requirements.
• Keeps subscribe-and-pay inside one continuously presented sheet, including initial-payment failure and retry, without the modal dismissal/reappearance gap.
• Retains the settled payment rail in completed request and subscription history so Lightning feedback is purple and on-chain feedback is orange, including success confetti.

This PR intentionally covers payer-side receipt only. Subscription creation, Discover, automatic payment without confirmation, and renewal are not included because they are outside this MVP or are not currently exposed by Paykit.

Dependencies:

• Paykit 0.1.0-rc46
• Payment proof delivery #683

Linked Issues/Tasks

• Figma subscriptions overview
• Android companion PR #1186

Screenshot / Video

Final iOS and cross-platform proof recordings were completed locally; they are not attached to the PR.

QA Notes

Manual Tests

• Receive an immediate-start private subscription proposal and verify review → payment → success stays in one continuously presented sheet.
• Exercise failed and uncertain initial payments and verify retry stays in the same sheet while the first period remains due.
• Complete Lightning and on-chain subscription payments and verify purple/orange success confetti and matching completed-payment icons.
• Receive a future-start proposal, trigger its due notification, and open the exact billing-period payment.
• Dismiss and reopen a due request from the bell queue and Payments tab, then pay it with fresh private payment details.
• Review active, expired, fixed-term, and open-ended subscription details and cancel an active subscription.

Automated Checks

• 97 focused PaykitPaymentRequestServiceTests and PaykitPaymentProofServiceTests
• E2E regtest Debug build for an arm64 iOS simulator
• Exact build installed and cold-launched on an iOS simulator
• SwiftFormat validation for all 13 changed Swift files
• Localization validation
• git diff --check

[greptile-apps]

Greptile Summary

Adds payer-side Paykit subscriptions, recurring billing-period requests, notification routing, and payment-proof association.

• Introduces subscription proposal, overview, detail, cancellation, and initial-payment UI.
• Extends Paykit request synchronization and persistence with recurring periods, due notifications, and retry state.
• Integrates subscription payments into the existing private send and payment-proof flows.

Confidence Score: 3/5

This PR should not merge until persisted proofs remain readable across upgrades and on-chain reconciliation prevents one transaction from proving multiple requests.

Existing pending-proof records can permanently block proof reconciliation after upgrade, while address-and-amount-only transaction matching can associate one payment with multiple billing periods.

Files Needing Attention: Bitkit/Services/PaykitPaymentProofService.swift

Important Files Changed

Filename	Overview
Bitkit/Services/PaykitPaymentProofService.swift	Adds period-specific and delayed on-chain proof handling, but breaks decoding of existing persisted proofs and can reuse one txid across requests.
Bitkit/Services/PaykitPaymentRequestService.swift	Expands request synchronization and manager state for recurring subscriptions, presentation, dismissal, cancellation, and notifications.
Bitkit/Services/PaykitSubscription.swift	Defines subscription recurrence, billing periods, persisted state, and notification scheduling.
Bitkit/Views/Subscriptions/SubscriptionsView.swift	Adds the subscription proposal, overview, detail, success, and cancellation interfaces.
Bitkit/Views/Wallets/Send/SendConfirmationView.swift	Integrates initial subscription payments and uncertain on-chain outcomes into the shared send flow.
Bitkit/AppScene.swift	Coordinates subscription notification routing, proposal presentation, and delayed on-chain attribution.

Sequence Diagram

sequenceDiagram
  participant Provider
  participant Paykit
  participant Manager as Request Manager
  participant UI as Subscription UI
  participant Send as Send Flow
  participant Proof as Proof Service
  Provider->>Paykit: Private subscription proposal
  Paykit->>Manager: Synchronize proposal
  Manager->>UI: Present review
  UI->>Manager: Accept subscription
  Manager->>Paykit: Accept request
  Manager->>Send: Open due billing period
  Send->>Proof: Prepare and mark payment started
  Send->>Proof: Complete payment
  Proof->>Paykit: Submit period-specific proof
  Proof-->>UI: Resolve success or retain retry state

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_{Reviews (1): Last reviewed commit: "feat: add Paykit subscription payments" | Re-trigger Greptile}