Add ecommerce analytics module (v0.2.0)

- 13 ecommerce event types with Swift actors for thread safety
- TolinkuItem model with Decimal precision for money values
- Automatic cart ID lifecycle via UserDefaults
- Event batching with UIKit background observer
- Updated README with ecommerce documentation

v0.1.2: Add event type validation and auto-prefix

Fix test failures on macOS CI

Initial release