Add Pico buzzer abstraction

tests/test_pico_core.py

@@ -628,3 +628,43 @@ def test_alarm_view_model_sensor_failure():
     assert alarm["severity"] == "warning"
     assert alarm["title"] == "Sensor Failure"
     assert alarm["detail"] == "Outside"
+
+
+class FakePin:
+    def __init__(self):
+        self.values = []
+
+    def value(self, value):
+        self.values.append(value)
+
+
+def test_buzzer_on_off():
+    from hardware.buzzer import Buzzer
+
+    pin = FakePin()
+    buzzer = Buzzer(pin)
+
+    buzzer.on()
+    assert buzzer.enabled is True
+    assert pin.values[-1] == 1
+
+    buzzer.off()
+    assert buzzer.enabled is False
+    assert pin.values[-1] == 0
+
+
+def test_buzzer_updates_from_alarm_view():
+    from hardware.buzzer import Buzzer
+    from ui.alarm_view_model import AlarmViewModel
+
+    buzzer = Buzzer()
+
+    buzzer.update_from_alarm_view(AlarmViewModel(["fridge_zone_1_high"]))
+
+    assert buzzer.enabled is True
+    assert buzzer.pattern == "critical"
+
+    buzzer.update_from_alarm_view(AlarmViewModel([]))
+
+    assert buzzer.enabled is False
+    assert buzzer.pattern is None