feat: accept allowance offers automatically on the allowee's wallet

[ovitrif]

Closes #807
Twin: synonymdev/bitkit-android#1385
Stacked on #799
Refs: #805

This PR makes the allowee's wallet accept an allowance the allower offers, so the allowee taps nothing and the allowance is active as soon as the offer arrives.

Description

• Adds automatic acceptance of a received allowance proposal that makes this wallet the allowee, so the allower's decision alone activates the allowance.
• Adds an "Allowance Added" notification, "{name} set up an allowance for you", with a toast fallback, so the allowee learns about the new allowance.
• Keeps the review sheet with Accept and Decline for an allowee's ask, because there the money is this wallet's.
• Retries a failed acceptance on the next refresh, and never touches a proposal this wallet sent or one already answered.

Out of Scope

• Bitkit/Resources/Localization: the new strings are English only until the next translation sync.
• Allowee-authored asks: this PR only changes what the allowee's wallet does with a received offer; the iOS app proposes allowances only as allower, so the review sheet for an ask is covered by unit tests, not on a device.

Design

N/A — no design available.

Preview

Payer waits	Payee: Allowance Added	Payee: Active	Payer: Active

Recording
07-side-by-side-payer-left-payee-right.mp4

QA Notes

Journeys

• updated set-and-accept.xml

Manual Tests

• 1. Payer: Allowances → Add Allowance → contact → Save: the payee's wallet shows no review sheet, posts "Allowance Added", and both rows turn Active — the first private link between two new contacts can delay the accept by a minute or two.
• 2. regression: payee: allowance detail → Swipe To End Allowance: ends on both sides.
• Allowee-authored ask → review sheet on the allower — not reachable on iOS, which proposes only as allower; covered by PaykitAllowanceExecutorTests.swift.

Automated Checks

• added PaykitAllowanceTests.swift — only a received proposal from the allower counts as an offer
• added PaykitAllowanceExecutorTests.swift — an allower's offer is accepted without the sheet and not announced twice; an allowee's ask still goes to the sheet; sent and answered proposals are never accepted
• ran xcodebuild test -only-testing:BitkitTests on an iPhone 17 simulator (iOS 26.5) with Paykit rc59 — 1,625 tests, 12 skipped, 0 failures
• ran the Paykit and allowance suites again after merging the updated feat: add allowances for automatic paykit payments #799 — 382 tests, 0 failures
• ran set-and-accept.xml on two simulators against the staging regtest backend: the payee turned Active with no tap about 95 s after the proposal arrived, no review sheet opened, and the toast "Allowance Added" showed (the system notification was not exercised, no permission prompt appeared)

[ovitrif]

Pushed 0b8e352: this PR now sits on the updated #799 (merge 8f0449c, Paykit SDK rc59 with identity-wide shared state).

• Rebased only this PR's two feature commits onto the new feat: add allowances for automatic paykit payments #799, whose old base commits are gone, and resolved the conflicts in AppScene.swift and the two allowance test files. Allowances are bound to identities now, so the offer rule is unchanged: a received proposal is accepted automatically only when this wallet is the allowee.
• README: the journeys README no longer promises a one-second accept; the offer is accepted once it has arrived, which can take a minute or two between contacts that have never exchanged a private message.
• Local verification: BitkitTests on an iPhone 17 simulator, 1,625 tests, 12 skipped, 0 failures; set-and-accept.xml on two simulators against staging regtest passed, the payee turned Active with no tap and no review sheet.
• The description now carries the screenshots and a recording, and its QA Notes record that the allowee-ask review sheet is not reachable on iOS.

[ovitrif]

Pushed 14307a0: merged the updated #799 (a19ea87: the request-presentation and covered-request fixes and more of Ben's shared-runtime merges) into this PR; the merge was clean and nothing in the auto-accept code changed.

Local verification: the Paykit and allowance suites on an iPhone 17 simulator, 382 tests, 0 failures.