feat: add contact payment UI

[ben-kaufman]

Description

Adds the contact-payment UI that was intentionally left out of the private Paykit PR:

• Send -> Contact selection with contact-aware send headers.
• Contact avatars in the main activity lists, while contact-specific activity lists keep the standard arrow icon.
• Activity detail contact assignment, assigned-contact display, and detach action.
• Settings -> General -> Payment Preference toggles for Lightning/on-chain payment methods and private/public contact-payment publishing.

This targets codex/paykit-private-payments so it can be reviewed separately from the private Paykit core work.

Linked Issues/Tasks

Refs #539

Screenshot / Video

Not attached in this PR body. The UI was validated locally against the simulator flow, and this branch is intentionally scoped to UI/wiring on top of the private payments branch.

Verification

• swiftformat --lint Bitkit/Services/PrivatePaykitService+Endpoints.swift Bitkit/ViewModels/SettingsViewModel.swift Bitkit/Views/Settings/General/PaymentPreferenceView.swift Bitkit/Views/Wallets/Activity/ActivityRow.swift Bitkit/Views/Wallets/Activity/ActivityItemView.swift Bitkit/Views/Wallets/Send/SendContactSelectView.swift Bitkit/Views/Wallets/Send/SendOptionsView.swift Bitkit/Views/Wallets/Send/SendSheet.swift Bitkit/Views/Wallets/Activity/AssignActivityContactView.swift Bitkit/Components/PubkyContactAvatar.swift Bitkit/Components/PubkyContactRow.swift
• git diff --check
• git diff --cached --check
• node scripts/validate-translations.js
• env DEVELOPER_DIR=/Users/benk10/Downloads/Old\ Mac\ Backup/Xcode.app/Contents/Developer xcodebuild -quiet -project Bitkit.xcodeproj -scheme Bitkit -configuration Debug -destination id=15FE6795-02FB-4073-A427-63F0B39A3A17 -derivedDataPath /private/tmp/bitkit-contact-ui-build build

[chatgpt-codex-connector]

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[ben-kaufman]

About 2, I guess this is mostly a design / UI choice.
About 3, I assume this is the intention with it no? Ie. it's meant for when we can't know which contact the payment belongs to, so user can manually assign it.

[piotr-iohk]

About 2, I guess this is mostly a design / UI choice.

Added comment in figma.

[piotr-iohk]

Initial testing with paykit rc6.

"Failed to send given payment" toast

Alice is iOS, Bob is Android.

Bob seems to be able to send to Alice (ln and onchain) however Alice has problems sending ln ("Failed to send given payment"), onchain seems to be ok.

Alice:
bitkit_logs_2026-05-18_15-42-28.zip

Bob:
logs.zip

Screen.Recording.2026-05-18.at.17.38.01.mov