feat: add interval projection schema and models

Add time-series tracking tables for animal location, tag, and attribute
history. Each interval represents a period when an animal had a specific
state, with open intervals (end_utc=NULL) for current state.

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

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

src/animaltrack/models/intervals.py

@@ -0,0 +1,44 @@
+# ABOUTME: Pydantic models for time-series interval tracking.
+# ABOUTME: Tracks animal location, tag, and attribute history over time.
+
+from typing import Literal
+
+from pydantic import BaseModel, Field
+
+
+class LocationInterval(BaseModel):
+    """Represents a period when an animal was at a specific location.
+
+    Open intervals (end_utc=None) indicate the animal is still at that location.
+    """
+
+    animal_id: str = Field(..., min_length=26, max_length=26)
+    location_id: str = Field(..., min_length=26, max_length=26)
+    start_utc: int
+    end_utc: int | None = None
+
+
+class TagInterval(BaseModel):
+    """Represents a period when an animal had a specific tag.
+
+    Open intervals (end_utc=None) indicate the tag is still active.
+    """
+
+    animal_id: str = Field(..., min_length=26, max_length=26)
+    tag: str
+    start_utc: int
+    end_utc: int | None = None
+
+
+class AttrInterval(BaseModel):
+    """Represents a period when an animal had a specific attribute value.
+
+    Tracks changes to sex, life_stage, repro_status, and status over time.
+    Open intervals (end_utc=None) indicate the current attribute value.
+    """
+
+    animal_id: str = Field(..., min_length=26, max_length=26)
+    attr: Literal["sex", "life_stage", "repro_status", "status"]
+    value: str
+    start_utc: int
+    end_utc: int | None = None