Implements Step 4.3 from the plan:
- Add selection/resolver.py with basic resolve_selection for validating
animal IDs exist and are alive
- Add ProductsProjection placeholder (stats tables added in Step 4.4)
- Add ProductService with collect_product() function
- Add PRODUCT_COLLECTED to EventAnimalsProjection for linking events
to affected animals
- Full test coverage for all new components
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
