feat(lib): add gaussian_smooth to _postprocess

tests/unit/test_postprocess.py

@@ -0,0 +1,25 @@
+"""Tests for trajectory post-processing primitives."""
+from __future__ import annotations
+
+import numpy as np
+
+from ai_mouse._postprocess import gaussian_smooth
+
+
+def test_gaussian_smooth_preserves_endpoints() -> None:
+    x = np.array([1.0, 5.0, 3.0, 8.0, 2.0, 6.0, 4.0])
+    result = gaussian_smooth(x, sigma=1.0)
+    assert result[0] == 1.0
+    assert result[-1] == 4.0
+
+
+def test_gaussian_smooth_short_input_unchanged() -> None:
+    x = np.array([1.0, 2.0, 3.0])
+    result = gaussian_smooth(x, sigma=1.0)
+    assert np.array_equal(result, x)
+
+
+def test_gaussian_smooth_constant_unchanged() -> None:
+    x = np.full(20, 7.5)
+    result = gaussian_smooth(x, sigma=1.0)
+    assert np.allclose(result, x, atol=1e-6)