feat: add reference tables schema and Pydantic models

Implements Step 1.4: Creates migration for species, locations, products,
feed_types, and users tables with full CHECK constraints. Adds Pydantic
models with validation for all reference types including enums for
ProductUnit and UserRole.

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

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

src/animaltrack/models/__init__.py

@@ -0,0 +1,22 @@
+# ABOUTME: Models package for AnimalTrack.
+# ABOUTME: Exports all Pydantic models and enums for reference data.
+
+from animaltrack.models.reference import (
+    FeedType,
+    Location,
+    Product,
+    ProductUnit,
+    Species,
+    User,
+    UserRole,
+)
+
+__all__ = [
+    "FeedType",
+    "Location",
+    "Product",
+    "ProductUnit",
+    "Species",
+    "User",
+    "UserRole",
+]

src/animaltrack/models/reference.py

@@ -0,0 +1,129 @@
+# ABOUTME: Pydantic models for reference tables (species, locations, products, feed_types, users).
+# ABOUTME: These models validate data before database insertion and provide type safety.
+
+from enum import Enum
+
+from pydantic import BaseModel, Field, field_validator
+
+
+class ProductUnit(str, Enum):
+    """Unit of measurement for products."""
+
+    PIECE = "piece"
+    KG = "kg"
+
+
+class UserRole(str, Enum):
+    """Role for system users."""
+
+    ADMIN = "admin"
+    RECORDER = "recorder"
+
+
+class Species(BaseModel):
+    """Animal species reference data."""
+
+    code: str
+    name: str
+    active: bool = True
+    created_at_utc: int
+    updated_at_utc: int
+
+    @field_validator("created_at_utc", "updated_at_utc")
+    @classmethod
+    def timestamp_must_be_non_negative(cls, v: int) -> int:
+        """Timestamps must be >= 0 (milliseconds since Unix epoch)."""
+        if v < 0:
+            msg = "Timestamp must be non-negative"
+            raise ValueError(msg)
+        return v
+
+
+class Location(BaseModel):
+    """Physical location reference data."""
+
+    id: str = Field(..., min_length=26, max_length=26)
+    name: str
+    active: bool = True
+    created_at_utc: int
+    updated_at_utc: int
+
+    @field_validator("id")
+    @classmethod
+    def id_must_be_26_chars(cls, v: str) -> str:
+        """Location ID must be exactly 26 characters (ULID format)."""
+        if len(v) != 26:
+            msg = "Location ID must be exactly 26 characters"
+            raise ValueError(msg)
+        return v
+
+    @field_validator("created_at_utc", "updated_at_utc")
+    @classmethod
+    def timestamp_must_be_non_negative(cls, v: int) -> int:
+        """Timestamps must be >= 0 (milliseconds since Unix epoch)."""
+        if v < 0:
+            msg = "Timestamp must be non-negative"
+            raise ValueError(msg)
+        return v
+
+
+class Product(BaseModel):
+    """Product reference data (eggs, meat, etc.)."""
+
+    code: str
+    name: str
+    unit: ProductUnit
+    collectable: bool
+    sellable: bool
+    active: bool = True
+    created_at_utc: int
+    updated_at_utc: int
+
+    @field_validator("created_at_utc", "updated_at_utc")
+    @classmethod
+    def timestamp_must_be_non_negative(cls, v: int) -> int:
+        """Timestamps must be >= 0 (milliseconds since Unix epoch)."""
+        if v < 0:
+            msg = "Timestamp must be non-negative"
+            raise ValueError(msg)
+        return v
+
+
+class FeedType(BaseModel):
+    """Feed type reference data."""
+
+    code: str
+    name: str
+    default_bag_size_kg: int = Field(..., ge=1)
+    protein_pct: float | None = None
+    active: bool = True
+    created_at_utc: int
+    updated_at_utc: int
+
+    @field_validator("created_at_utc", "updated_at_utc")
+    @classmethod
+    def timestamp_must_be_non_negative(cls, v: int) -> int:
+        """Timestamps must be >= 0 (milliseconds since Unix epoch)."""
+        if v < 0:
+            msg = "Timestamp must be non-negative"
+            raise ValueError(msg)
+        return v
+
+
+class User(BaseModel):
+    """System user reference data."""
+
+    username: str
+    role: UserRole
+    active: bool = True
+    created_at_utc: int
+    updated_at_utc: int
+
+    @field_validator("created_at_utc", "updated_at_utc")
+    @classmethod
+    def timestamp_must_be_non_negative(cls, v: int) -> int:
+        """Timestamps must be >= 0 (milliseconds since Unix epoch)."""
+        if v < 0:
+            msg = "Timestamp must be non-negative"
+            raise ValueError(msg)
+        return v