feat: add allowances for automatic paykit payments

[ovitrif]

Depends on pubky/paykit-rs#161 (open; head 8b893f0, the top of the #158 → #159 → #160 → #161 stack). The Xcode project points at a local checkout of pubky/paykit-rs beside this one (../paykit-rs) that builds the Swift bindings and xcframework from that head, instead of the published 0.1.0-rc55 tag, so CI cannot build this branch until #161 is published.

Stacked on #798: the allowance tests prove that admission ignores the demo clock, so the branch starts from that commit and GitHub retargets this PR to master when it merges.

Android port: synonymdev/bitkit-android#1340

This PR adds allowances: a payer sets a per-payment and a monthly limit for a Paykit contact, and that contact's requests within the limits are paid without asking.

Description

• Adds an Allowances tab to Subscriptions, with an empty state, the list and a Set Allowance sheet with per-payment and monthly USD limits, so a payer can let a contact's requests pay themselves
• Sends the allowance over the existing private Paykit link and opens a review sheet on the receiver, who accepts or declines; either side can end an allowance from its detail sheet
• Pays an incoming request within the limits automatically over Lightning: the request is reserved in the SDK's allowance accounting before the send and reported back afterwards, so a kill and relaunch mid-payment never pays twice
• Leaves a request above the per-payment limit, over the monthly cap, or after an end as an ordinary Payment Request, with a Limit Reached notification for the payer and a Payment Executed notification for an automatic one; requests that arrived before the allowance stay manual
• Attributes automatically paid activity to the contact, tags those rows "Auto-paid" in the Payments tab and shows the amount paid automatically on the allowance detail
• Keeps Paykit state written by rc55 readable: the stored blob is probed on first launch and converted between the rc55 and allowance layouts, so an upgrade or a downgrade keeps the profile, contacts and requests, and a wallet without an allowance ledger is left untouched at launch
• Counts allowance months from the original anchor, so the monthly cap resets on the same day each month
• Waits for the payee's next private payment list instead of asking the payer when the previous list was used up, and holds automatic payments until the node has a usable channel, because both cases fell back to manual on regtest

Out of Scope

• Allowance detail on the payee: "Paid automatically" counts only the payer's own journal, so the payee sees $0.00; SDK follow-up
• Automatic payments: Lightning only, with no capacity check before choosing bolt11 and no on-chain fallback, so a payer without a usable channel falls back to a manual request
• Failed automatic send: the request is already accepted, so it falls back to a manual Payment Request and is not retried automatically
• Paykit dependency: stays on the local build of Expose Allowance accounting to Swift and Kotlin pubky/paykit-rs#161 until it is published

Design

Figma "Bitkit - Experimental New": Allowances empty state, Set Allowance, Allowances list. The receiver's review sheet and the detail sheet have no frame and follow the drawn film. Deliberate differences: the first tab stays "Overview", the list row's right column reads the monthly limit, and the copy typos are fixed.

Preview

Screenshots follow before review.

QA Notes

Journeys

• new set-and-accept.xml — the offer opens on the payee by itself and both rows turn Active
• new auto-pay-under-limit.xml — a $2 request pays itself with only a Payment Executed notification
• new above-limit-asks.xml — a $20 request arrives as an ordinary Payment Request
• new monthly-cap-reached.xml — the third $4 request on a $10 cap raises Limit Reached and asks
• new end-stops-auto-pay.xml — after either side ends it, the next request asks
• new restart-never-pays-twice.xml — a kill right after the hand-off never leads to a second payment

Manual Tests

• 1. regression: install the rc55 build, create a profile and a contact, then install this build → Profile and Contacts: intact, log reads "Resolved the stored Paykit state layout as 'RC55'"
• 2. restart-never-pays-twice.xml and the payee half of end-stops-auto-pay.xml on two simulators: the source run drove them on Android only; iOS covered set, accept, auto-pay, ask above the limit and end by the payer

Automated Checks

• added PaykitAllowanceTests.swift — limits, terms, capacity, month anchoring and admission decisions, including that admission ignores the demo clock
• added PaykitAllowanceExecutorTests.swift — reserve, hand-off, outcome recording, deferral, channel readiness and restart recovery of automatic payments
• updated PaykitPaymentProofServiceTests.swift — payment proofs carry the allowance id
• updated PaykitPaymentRequestServiceTests.swift — pre-allowance requests stay manual
• ran xcodebuild test -only-testing:BitkitTests on an iPhone simulator against the local Paykit build — 1,411 tests pass, 12 skipped; CI cannot resolve the Paykit build until Expose Allowance accounting to Swift and Kotlin pubky/paykit-rs#161 is published