feat: add release notes for v1.0.0 with core features and milestones

Author: Kapusch

Docs/Release-1.0.0.md

@@ -0,0 +1,54 @@
+# Release Notes: Kapusch.StoreKit2.iOS v1.0.0
+
+**Release Date**: March 8, 2026  
+**Status**: Release Candidate (RC) — v1.0.0-rc.1  
+**Previous Version**: 0.1.0  
+**NuGet Package**: [Kapusch.StoreKit2.iOS](https://www.nuget.org/packages/Kapusch.StoreKit2.iOS/)
+
+---
+
+## Overview
+
+v1.0.0 marks the first **stable production release** of the StoreKit 2 iOS interop wrapper. This release promotes the library from pre-release status (0.1.0) to a production-ready API with comprehensive StoreKit 2 purchase, restoration, and subscription management capabilities.
+
+### Key Milestones
+
+- **Full StoreKit 2 API coverage**: Purchase, restore, entitlements, and transaction listeners
+- **Stable managed API**: Public interfaces locked for v1.0.0 compatibility
+- **Production-ready native wrapper**: Swift interop compiled for iOS device and simulator architectures
+- **NuGet.org availability**: Published to official NuGet.org registry
+
+---
+
+## What's New in v1.0.0
+
+### Core Features (Completed in 0.x → 1.0)
+
+#### 1. **Purchase Flow**
+- `IStoreKit2BillingClient.PurchaseAsync()` — perform a standard purchase
+- Direct integration with StoreKit 2 request/listener pattern
+- Full `CancellationToken` support for async cancellation
+
+#### 2. **Promotional Offers**
+- `IStoreKit2BillingClient.PurchaseWithPromotionalOfferAsync()` — purchase with promo code
+- `StoreKitPromotionalOfferSignature` — managed representation of offer metadata
+- Seamless interop with StoreKit 2 promotional flow
+
+#### 3. **Restoration & Entitlements**
+- `IStoreKit2BillingClient.RestoreAsync()` — restore previously purchased products
+- `IStoreKit2BillingClient.GetCurrentEntitlementsAsync()` — query active entitlements
+- Both methods support product ID filtering
+
+#### 4. **Offer Metadata**
+- `IStoreKit2BillingClient.GetOfferMetadataAsync()` — retrieve intro offer details
+- `StoreKitOfferMetadata` — structured offer pricing and period information
+- Support for intro offers and subscription pricing tiers
+
+#### 5. **Transaction Updates (Passive & Active)**
+- `IStoreKit2BillingClient.EnsureTransactionUpdatesListenerStarted()` — singleton long-lived listener to StoreKit 2 `Transaction.updates`
+- `IStoreKit2BillingClient.SubscribeToTransactionUpdates()` — subscribe to verified transaction callbacks
+- Supports both passive (background) and active (in-app) scenarios
+
+#### 6. **Entitlements Support** 
+- Passive entitlements API for background validation
+- Promotional purchase APIs for flexible offer flows