feat(Q5): NOAA sunset calculator (stdlib only)

tests/unit/test_solar.py

@@ -0,0 +1,18 @@
+import datetime
+from vigilar.detection.solar import get_sunset
+
+
+def test_sunset_returns_time():
+    result = get_sunset(45.0, -85.0, datetime.date(2026, 6, 21))
+    assert isinstance(result, datetime.time)
+
+
+def test_sunset_equator():
+    result = get_sunset(0.0, 0.0, datetime.date(2026, 3, 20))
+    assert 17 <= result.hour <= 19
+
+
+def test_sunset_different_dates_vary():
+    d1 = get_sunset(45.0, -85.0, datetime.date(2026, 3, 1))
+    d2 = get_sunset(45.0, -85.0, datetime.date(2026, 9, 1))
+    assert d1 != d2