App Store Server API + CloudKit Push Notifications + Auto-Release

[meszmate]

Summary

• Add complete App Store Server API support behind a new opt-in appstore feature — 23 endpoints covering transactions, subscriptions, consumption, refund history, notifications, retention messaging, and JWS signed data verification with X.509 certificate chain validation
• Add CloudKit push notification support — APNs payload parsing for query/zone/database notifications and webcourier long-polling
• Add GitHub Actions release workflow that validates, publishes to crates.io, and creates a GitHub release on tag push
• Update CI and README with full documentation for all new features

App Store Server API (appstore feature)

New opt-in feature (appstore = ["chrono", "x509-cert"]) with 13 modules:

• types.rs — 30+ enums (environment, status, notification types, consumption, etc.)
• error.rs — 78 error codes with AppStoreErrorCode enum and error parsing
• models.rs — 25+ request/response structs
• client.rs — AppStoreServerClient with JWT Bearer auth (aud: appstoreconnect-v1)
• transactions.rs — 5 endpoints: history (v1/v2), info, order lookup, app transaction
• subscriptions.rs — 4 endpoints: status, extend, mass extend, mass extend status
• consumption.rs — 3 endpoints: consumption data, refund history, app account token
• notifications.rs — 3 endpoints: test notification, test status, notification history
• messaging.rs — 8 endpoints: image/message CRUD, default message config
• signed_data.rs — SignedDataVerifier with X.509 chain validation, JWS decode
• notifications_v2.rs — V2 notification payload types (19 types, 17 subtypes)
• notifications_v1.rs — V1 notification payload types (deprecated)

CloudKit Push Notifications

• New cloudkit::notifications module with CKNotification enum (Query, RecordZone, Database variants)
• parse_notification() for parsing APNs ck dictionary payloads
• CloudKitClient::poll_notifications() for webcourier long-polling (120s timeout)
• QueryNotificationReason and DatabaseScope enums
• 7 new fields on NotificationInfo (collapse ID, desired keys, category, title/subtitle localization)

CI/CD

• New release.yml workflow: triggered on v* tag push, runs validation, publishes to crates.io, creates GitHub release with auto-generated notes
• Updated ci.yml to include appstore feature in clippy, test, and check matrices