Add licensed variable product support for duration-based licenses (v0.5.3)

Customers can now purchase licenses with different durations (monthly,
yearly, lifetime) through WooCommerce product variations. Each variation
can have its own license validity settings.

New features:
- LicensedVariableProduct class for variable licensed products
- LicensedProductVariation class for individual variations
- Per-variation license duration and max activations settings
- Duration labels in checkout (Monthly, Quarterly, Yearly, etc.)
- Full support for WooCommerce Blocks checkout with variations
- Updated translations for German (de_CH)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,25 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.5.3] - 2026-01-26
+
+### Added
+
+- Variable licensed product type (`licensed-variable`) for selling licenses with different durations
+- Support for monthly, yearly, quarterly, or lifetime license variations
+- `LicensedVariableProduct` class extending `WC_Product_Variable`
+- `LicensedProductVariation` class for individual variation license settings
+- Variation-specific license duration settings in product edit page
+- Duration labels displayed in checkout domain fields (e.g., "Yearly License")
+- Variation ID tracking in order domain meta for proper license generation
+
+### Changed
+
+- Updated `LicenseManager::generateLicense()` to accept optional variation ID
+- Checkout now handles variations with separate domain fields per product/variation
+- WooCommerce Blocks checkout updated to display variation duration labels
+- Store API extension updated to include variation_id in domain data schema
+
 ## [0.5.2] - 2026-01-26
 
 ### Added