feat: add animal registry schema and models

Add database tables for animal tracking:
- animal_registry: main snapshot table with all animal attributes
- live_animals_by_location: denormalized view for fast roster queries
- animal_aliases: merge tracking for when animals are discovered to be same

Includes Pydantic models and comprehensive tests for all constraints.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/animaltrack/models/animals.py

@@ -0,0 +1,61 @@
+# ABOUTME: Pydantic models for animal tracking tables.
+# ABOUTME: Includes Animal, LiveAnimal, and AnimalAlias for registry system.
+
+from pydantic import BaseModel, Field
+
+from animaltrack.events.enums import AnimalStatus, LifeStage, Origin, ReproStatus, Sex
+
+
+class Animal(BaseModel):
+    """Full animal record from animal_registry table.
+
+    Represents the current state of an animal including all attributes,
+    location, and lifecycle status.
+    """
+
+    animal_id: str = Field(..., min_length=26, max_length=26)
+    species_code: str
+    identified: bool = False
+    nickname: str | None = None
+    sex: Sex
+    repro_status: ReproStatus
+    life_stage: LifeStage
+    status: AnimalStatus
+    location_id: str = Field(..., min_length=26, max_length=26)
+    origin: Origin
+    born_or_hatched_at: int | None = None
+    acquired_at: int | None = None
+    first_seen_utc: int
+    last_event_utc: int
+
+
+class LiveAnimal(BaseModel):
+    """Animal record from live_animals_by_location table.
+
+    Denormalized view of active animals for fast roster queries.
+    Only includes animals with status='alive'.
+    """
+
+    animal_id: str = Field(..., min_length=26, max_length=26)
+    location_id: str = Field(..., min_length=26, max_length=26)
+    species_code: str
+    identified: bool = False
+    nickname: str | None = None
+    sex: Sex
+    repro_status: ReproStatus
+    life_stage: LifeStage
+    first_seen_utc: int
+    last_move_utc: int | None = None
+    tags: list[str] = []
+
+
+class AnimalAlias(BaseModel):
+    """Merge tracking record from animal_aliases table.
+
+    When two animals are discovered to be the same individual,
+    one becomes an alias pointing to the survivor.
+    """
+
+    alias_animal_id: str = Field(..., min_length=26, max_length=26)
+    survivor_animal_id: str = Field(..., min_length=26, max_length=26)
+    merged_at_utc: int