Implements Step 2.3 of the plan:
- 17 Pydantic payload models for all event types per spec §6
- 6 enums: Sex, ReproStatus, LifeStage, AnimalStatus, Origin, Outcome
- Tag normalization per spec §20 (lowercase, spaces→hyphens, max 32 chars)
- ULID validation utilities
- 38 tests covering payloads, enums, and tag normalization
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
