refactor: styles own their ringing tone directly (Pattern C)

Drop the injected AlarmSound Protocol and the wecker.Sound class. Each style
now owns its tone by using pygame directly; the runner owns only the audio
engine lifecycle (mixer init/quit), button sampling, and cleanup. This is the
seam for future styles that handle their own tone — a 'talk' style would just
import pygame and play speech, with no shared interface to extend.

- styles/base.py: AlarmStyle.__init__(set_led, music_file) + start() + update()
- styles/blink.py: start() loads+plays music via pygame.mixer.music
- styles/simple.py: owns its beep — synthesises a square-wave buffer in
  module (stdlib array+math) and plays it via pygame.mixer.Sound
- wecker.py: setup() brings up the mixer only; run_alarm constructs the style
  and guards start() with a clean log+exit on failure

Tests: a shared tests/conftest.py stubs RPi.GPIO/pygame in sys.modules before
any SUT import (order-independent, removes duplicated inline mocking); the
wecker mock_pygame fixture patches one fresh pygame mock into wecker + both
style modules so assertions see the same calls.

README: tone-ownership and plugin-contract updated.

tests/test_wecker.py

@@ -1,13 +1,9 @@
 import pytest
-import sys
 from unittest.mock import MagicMock, patch
 
-# Mock RPi.GPIO and pygame before importing wecker
-sys.modules["RPi"] = MagicMock()
-sys.modules["RPi.GPIO"] = MagicMock()
-sys.modules["pygame"] = MagicMock()
-
-import wecker  # noqa: E402
+import styles.blink
+import styles.simple
+import wecker
 
 
 @pytest.fixture
@@ -20,7 +16,18 @@ def mock_gpio():
 
 @pytest.fixture
 def mock_pygame():
-    with patch.object(wecker, "pygame") as mock:
+    """One fresh pygame mock shared by wecker and both styles.
+
+    Under Pattern C the styles use pygame directly, so a single mock must be
+    patched into wecker (setup) and the style modules (start) for assertions
+    to see the same calls.
+    """
+    mock = MagicMock()
+    with (
+        patch.object(wecker, "pygame", mock),
+        patch.object(styles.blink, "pygame", mock),
+        patch.object(styles.simple, "pygame", mock),
+    ):
         yield mock
 
 
@@ -50,7 +57,7 @@ def test_run_alarm_unknown_style_raises(mock_gpio, mock_pygame):
 
 
 def test_run_alarm_uses_selected_style(mock_gpio, mock_pygame):
-    """run_alarm looks up the style, injects a Sound, and calls start()."""
+    """run_alarm looks up the style, injects set_led + music_file, calls start()."""
     fake = MagicMock()
     fake.update.return_value = True  # keep ringing
     fake_style_cls = MagicMock(return_value=fake)
@@ -61,7 +68,7 @@ def test_run_alarm_uses_selected_style(mock_gpio, mock_pygame):
     get_style.assert_called_once_with("whatever")
     args = fake_style_cls.call_args.args
     assert args[0] is wecker.set_led
-    assert isinstance(args[1], wecker.Sound)
+    assert isinstance(args[1], str)  # resolved music file
     fake.start.assert_called_once()
     fake.update.assert_called()
 
@@ -73,7 +80,7 @@ def test_run_alarm_default_music_file(mock_gpio, mock_pygame, monkeypatch):
     fake_style_cls = MagicMock(return_value=fake)
     with patch("wecker.get_style", return_value=fake_style_cls):
         wecker.run_alarm(test_mode=True)
-    assert fake_style_cls.call_args.args[2] == wecker.DEFAULT_MUSIC_FILE
+    assert fake_style_cls.call_args.args[1] == wecker.DEFAULT_MUSIC_FILE
 
 
 def test_run_alarm_env_music_file(mock_gpio, mock_pygame, monkeypatch):
@@ -83,7 +90,7 @@ def test_run_alarm_env_music_file(mock_gpio, mock_pygame, monkeypatch):
     fake_style_cls = MagicMock(return_value=fake)
     with patch("wecker.get_style", return_value=fake_style_cls):
         wecker.run_alarm(test_mode=True)
-    assert fake_style_cls.call_args.args[2] == "/env/track.mp3"
+    assert fake_style_cls.call_args.args[1] == "/env/track.mp3"
 
 
 def test_run_alarm_music_file_arg_overrides_env(mock_gpio, mock_pygame, monkeypatch):
@@ -93,11 +100,10 @@ def test_run_alarm_music_file_arg_overrides_env(mock_gpio, mock_pygame, monkeypa
     fake_style_cls = MagicMock(return_value=fake)
     with patch("wecker.get_style", return_value=fake_style_cls):
         wecker.run_alarm(music_file="/arg/track.mp3", test_mode=True)
-    assert fake_style_cls.call_args.args[2] == "/arg/track.mp3"
+    assert fake_style_cls.call_args.args[1] == "/arg/track.mp3"
 
 
-@patch("wecker.time.time")
-def test_run_alarm_blink_plays_music(mock_time, mock_gpio, mock_pygame):
+def test_run_alarm_blink_plays_music(mock_gpio, mock_pygame):
     """The default (blink) style plays music on an endless loop."""
     wecker.run_alarm(test_mode=True)
     assert mock_pygame.mixer.music.play.called
@@ -109,18 +115,3 @@ def test_run_alarm_simple_beeps_and_plays_no_music(mock_gpio, mock_pygame):
     wecker.run_alarm(style_name="simple", test_mode=True)
     assert mock_pygame.mixer.Sound.return_value.play.called  # beep played
     assert not mock_pygame.mixer.music.play.called  # no music
-
-
-def test_sound_play_music_loads_and_loops(mock_pygame):
-    s = wecker.Sound()
-    s.play_music("/track.mp3")
-    mock_pygame.mixer.music.load.assert_called_with("/track.mp3")
-    mock_pygame.mixer.music.set_volume.assert_called_with(1.0)
-    mock_pygame.mixer.music.play.assert_called_with(-1)
-
-
-def test_sound_play_beep_plays_buffer(mock_pygame):
-    s = wecker.Sound()
-    s.play_beep()
-    mock_pygame.mixer.Sound.assert_called_once_with(wecker._BEEP_BUFFER)
-    mock_pygame.mixer.Sound.return_value.play.assert_called_once()