Redesign subscription catalog and transaction runtime

[lynnswap]

Purpose

Introduce a typed, app-domain subscription catalog and complete the beta API redesign around TransactionStore, entitlement availability, transaction policy, and deterministic testing.

Changes

• Add AutoRenewableSubscriptionGroup, AutoRenewableSubscriptionCatalog, StoreSubscriptions, and StoreSubscription for typed Product ID-to-entitlement declarations.
• Rework TransactionStore around explicit entitlement availability, exact isEntitled(to:) queries, app-controlled overrides, optional delegate policies, and process-owned lifecycle/finish authority.
• Strengthen reconciliation, restore, cancellation, failure ownership, reentrancy, and shutdown behavior with deterministic runtime coverage.
• Add StoreTransactionKitTesting, including a synthetic purchase harness and manually advanced test clock.
• Update the external consumer fixture, CI, README, and DocC for the new public contract.
• Migrate the app-hosted StoreKit suite to Tier 1/Tier 2 monthly and yearly subscriptions, including a catalog-external subscription group for live unmanaged transaction handling.

Testing

• Xcode 26.5 Swift package tests: 102 passed.
• Xcode 27 Swift package tests: 78 production and 24 testing tests passed.
• App-hosted StoreKit tests: 18/18 passed on Xcode 26.5 with iOS 18.6 and 18/18 passed on Xcode 27 with iOS 27.
• App-hosted test bundle cross-builds passed for iOS, tvOS, watchOS, and visionOS.
• External consumer fixture test passed.
• Release build passed.
• DocC archive passed with warnings treated as errors.
• swift-format, actionlint, workflow SHA pinning, and git diff --check passed.

Screenshots

Not applicable; this changes framework APIs, documentation, and automated tests.

[lynnswap]

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