feat: styles own their ringing tone (simple beeps, blink plays music)

Move audio ownership out of the shared runner and into each style via an
injected Sound capability (play_music(path) / play_beep()). The runner now
only owns button sampling and cleanup; the style kicks off its own tone in
start() and drives the LED.

- simple: a repeating square-wave beep (ordinary alarm-clock tone), no music
  file required. The beep is synthesised in memory as signed-16-bit stereo
  PCM (stdlib array+math) and played via pygame.mixer.Sound — no shipped
  audio asset, no new dependency.
- blink: unchanged behaviour — music on an endless loop from --music-file /
  MUSIC_FILE / the default track, via pygame.mixer.music.
- AlarmStyle contract gains sound + music_file in __init__ and a start()
  lifecycle hook; AlarmSound Protocol documents the audio seam for future
  styles that handle their own tone.
- setup() no longer loads music (that is the style's job now).

README updated: per-style ringing tone, the --music-file note (blink only),
and the extended plugin contract.

wecker.py

@@ -1,10 +1,13 @@
-import RPi.GPIO as GPIO
-import time
-import logging
-import pygame
-import sys
+import array
+import math
 import os
+import sys
+import time
 import fcntl
+import logging
+
+import pygame
+import RPi.GPIO as GPIO
 
 # Use PulseAudio/PipeWire audio driver to avoid ALSA device-busy errors.
 os.environ.setdefault("SDL_AUDIODRIVER", "pulse")
@@ -69,11 +72,12 @@ LED_PIN = 27
 DEFAULT_MUSIC_FILE = "Laid Back - Sunshine Reggae.mp3"
 
 
-def setup(music_file: str | None = None):
-    """Initialize GPIO and audio hardware. Call once before running."""
-    if music_file is None:
-        music_file = os.environ.get("MUSIC_FILE", DEFAULT_MUSIC_FILE)
+def setup():
+    """Initialize GPIO and audio hardware. 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.
+    """
     GPIO.setmode(GPIO.BCM)
     GPIO.setup(LED_PIN, GPIO.OUT)
     GPIO.setup(BUTTON_PIN, GPIO.IN, pull_up_down=GPIO.PUD_UP)
@@ -82,14 +86,47 @@ def setup(music_file: str | None = None):
     pygame.mixer.pre_init(frequency=44100, size=-16, channels=2, buffer=4096)
     pygame.mixer.init()
 
-    try:
-        pygame.mixer.music.load(music_file)
-        pygame.mixer.music.set_volume(1.0)
-    except Exception as e:
-        logging.error(f"Error loading audio file: {e}")
-        # Don't exit in test mode
-        if "pytest" not in sys.modules:
-            sys.exit(1)
+
+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):
@@ -108,16 +145,18 @@ def run_alarm(
 ):
     """Run the alarm clock with the given style until the style signals stop.
 
-    The runner owns everything shared (music loop, button sampling, cleanup);
-    the style only decides when to stop and what the LED does.
+    The runner owns only the shared button sampling and cleanup; each style
+    owns its own ringing tone (via the injected ``Sound``) and LED behaviour.
     """
-    style = get_style(style_name)(set_led)
-    setup(music_file=music_file)
-    logging.info("Alarm clock started. Music is playing in an endless loop.")
-    if "pygame" in globals() and hasattr(pygame, "mixer") and pygame.mixer.get_init():
-        pygame.mixer.music.play(-1)
+    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)
 
-    set_led(False)  # LED off at start; the style drives it from here.
+    setup()
+    sound = Sound()
+    style = style_cls(set_led, sound, music_file)
+    logging.info("Alarm clock started.")
+    style.start()  # style kicks off its own tone + initial LED
 
     try:
         while True:
@@ -146,7 +185,7 @@ if __name__ == "__main__":
     parser.add_argument(
         "--music-file",
         default=os.environ.get("MUSIC_FILE", DEFAULT_MUSIC_FILE),
-        help="Path to the MP3 file to play (default: $MUSIC_FILE or default track).",
+        help="Music file for the blink style (default: $MUSIC_FILE or default track).",
     )
     parser.add_argument(
         "--style",