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.

wecker.py

@@ -1,5 +1,3 @@
-import array
-import math
 import os
 import sys
 import time
@@ -73,10 +71,10 @@ DEFAULT_MUSIC_FILE = "Laid Back - Sunshine Reggae.mp3"
 
 
 def setup():
-    """Initialize GPIO and audio hardware. Call once before running.
+    """Initialize GPIO and the audio engine. Call once before running.
 
-    Audio playback itself is owned by each style via the injected ``Sound``
-    capability, so this only brings up the mixer and pins.
+    Each style owns its own ringing tone via pygame directly; this only brings
+    up the mixer and the GPIO pins.
     """
     GPIO.setmode(GPIO.BCM)
     GPIO.setup(LED_PIN, GPIO.OUT)
@@ -87,48 +85,6 @@ def setup():
     pygame.mixer.init()
 
 
-def _make_beep_buffer(
-    freq: int = 1000, duration: float = 0.15, rate: int = 44100
-) -> bytes:
-    """Synthesize a short square-wave beep as signed-16-bit stereo PCM.
-
-    Matches the mixer format from ``pre_init`` (rate, -16, 2 channels) so it
-    feeds straight into ``pygame.mixer.Sound``. No audio file, no extra dep.
-    """
-    n = int(rate * duration)
-    buf = array.array("h")
-    for i in range(n):
-        v = 32767 if math.sin(2 * math.pi * freq * (i / rate)) >= 0 else -32767
-        buf.append(v)
-        buf.append(v)  # duplicate to stereo
-    return buf.tobytes()
-
-
-_BEEP_BUFFER = _make_beep_buffer()
-
-
-class Sound:
-    """Audio capability injected into styles so each can own its ringing tone."""
-
-    def __init__(self):
-        self._beep = pygame.mixer.Sound(_BEEP_BUFFER)
-
-    def play_music(self, path: str):
-        """Load and play a music file on an endless loop."""
-        try:
-            pygame.mixer.music.load(path)
-            pygame.mixer.music.set_volume(1.0)
-            pygame.mixer.music.play(-1)
-        except Exception as e:
-            logging.error(f"Error loading audio file: {e}")
-            if "pytest" not in sys.modules:
-                sys.exit(1)
-
-    def play_beep(self):
-        """Play one short beep tone."""
-        self._beep.play()
-
-
 def set_led(on):
     """Turns the LED on or off (LOW = ON, HIGH = OFF)"""
     if "GPIO" in globals() and hasattr(GPIO, "output"):
@@ -145,18 +101,24 @@ def run_alarm(
 ):
     """Run the alarm clock with the given style until the style signals stop.
 
-    The runner owns only the shared button sampling and cleanup; each style
-    owns its own ringing tone (via the injected ``Sound``) and LED behaviour.
+    The runner owns only the audio engine lifecycle (mixer init/quit), button
+    sampling, and cleanup; each style owns its own ringing tone (via pygame
+    directly) and LED behaviour.
     """
     style_cls = get_style(style_name)  # validate before touching hardware
     if music_file is None:
         music_file = os.environ.get("MUSIC_FILE", DEFAULT_MUSIC_FILE)
 
     setup()
-    sound = Sound()
-    style = style_cls(set_led, sound, music_file)
+    style = style_cls(set_led, music_file)
     logging.info("Alarm clock started.")
-    style.start()  # style kicks off its own tone + initial LED
+    try:
+        style.start()  # style kicks off its own tone + initial LED
+    except Exception:
+        logging.exception("Error starting alarm")
+        if "pytest" not in sys.modules:
+            sys.exit(1)
+        raise
 
     try:
         while True: