Add audio resampling utility and scipy dependency

- Created resample_audio.py utility script
  - Automatically reads target sample rate from config.json
  - Resamples all WAV files in sounds directory
  - Creates .backup files before modifying originals
  - Handles both mono and stereo audio
  - Uses scipy.signal.resample for high-quality resampling

- Added scipy>=1.7.0 dependency to pyproject.toml
- Updated Makefile sync command to include scipy
- Updated README.md with sample rate troubleshooting section
- Updated config example in README to show 48kHz default
- Added beep_sound configuration to README system section

This resolves sample rate mismatch errors when audio files
don't match the configured rate in config.json.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

resample_audio.py

@@ -0,0 +1,151 @@
+#!/usr/bin/env python3
+"""
+Audio Resampling Utility for Wedding Phone
+Resamples all WAV files in sounds directory to match configured sample rate
+"""
+
+import wave
+import numpy as np
+import os
+import json
+from scipy import signal
+
+def load_config():
+    """Load sample rate from config.json"""
+    config_path = 'config.json'
+    if not os.path.exists(config_path):
+        print("config.json not found, using 48000Hz as default")
+        return 48000
+
+    with open(config_path, 'r') as f:
+        config = json.load(f)
+        return config['audio']['sample_rate']
+
+def resample_wav(input_file, output_file, target_rate):
+    """Resample a WAV file to target sample rate"""
+    try:
+        # Open source file
+        with wave.open(input_file, 'rb') as wf:
+            n_channels = wf.getnchannels()
+            sampwidth = wf.getsampwidth()
+            source_rate = wf.getframerate()
+            n_frames = wf.getnframes()
+
+            # Read audio data
+            audio_data = wf.readframes(n_frames)
+
+            # Convert to numpy array
+            if sampwidth == 1:
+                dtype = np.uint8
+            elif sampwidth == 2:
+                dtype = np.int16
+            elif sampwidth == 4:
+                dtype = np.int32
+            else:
+                print(f"Unsupported sample width: {sampwidth}")
+                return False
+
+            audio_array = np.frombuffer(audio_data, dtype=dtype)
+
+            # Handle stereo
+            if n_channels == 2:
+                audio_array = audio_array.reshape(-1, 2)
+
+            # Resample
+            if source_rate != target_rate:
+                print(f"  Resampling from {source_rate}Hz to {target_rate}Hz...")
+                num_samples = int(len(audio_array) * target_rate / source_rate)
+
+                if n_channels == 1:
+                    resampled = signal.resample(audio_array, num_samples)
+                else:
+                    # Resample each channel separately
+                    left = signal.resample(audio_array[:, 0], num_samples)
+                    right = signal.resample(audio_array[:, 1], num_samples)
+                    resampled = np.column_stack((left, right))
+
+                # Convert back to original dtype
+                resampled = np.clip(resampled, np.iinfo(dtype).min, np.iinfo(dtype).max)
+                audio_array = resampled.astype(dtype)
+
+            # Write output file
+            with wave.open(output_file, 'wb') as wf_out:
+                wf_out.setnchannels(n_channels)
+                wf_out.setsampwidth(sampwidth)
+                wf_out.setframerate(target_rate)
+                wf_out.writeframes(audio_array.tobytes())
+
+            return True
+
+    except Exception as e:
+        print(f"  Error: {e}")
+        return False
+
+def main():
+    """Main resampling function"""
+    print("Wedding Phone Audio Resampler")
+    print("=" * 50)
+
+    # Load target sample rate
+    target_rate = load_config()
+    print(f"\nTarget sample rate: {target_rate}Hz")
+
+    # Check sounds directory
+    sounds_dir = './rotary_phone_data/sounds'
+    if not os.path.exists(sounds_dir):
+        print(f"\nSounds directory not found: {sounds_dir}")
+        return
+
+    # Get all WAV files
+    wav_files = [f for f in os.listdir(sounds_dir) if f.endswith('.wav')]
+
+    if not wav_files:
+        print("\nNo WAV files found in sounds directory")
+        return
+
+    print(f"\nFound {len(wav_files)} WAV file(s)")
+    print("-" * 50)
+
+    # Process each file
+    for filename in wav_files:
+        input_path = os.path.join(sounds_dir, filename)
+        print(f"\nProcessing: {filename}")
+
+        # Check current sample rate
+        try:
+            with wave.open(input_path, 'rb') as wf:
+                current_rate = wf.getframerate()
+                print(f"  Current rate: {current_rate}Hz")
+
+                if current_rate == target_rate:
+                    print(f"  ✓ Already at {target_rate}Hz, skipping")
+                    continue
+        except Exception as e:
+            print(f"  Error reading file: {e}")
+            continue
+
+        # Create backup
+        backup_path = input_path + '.backup'
+        if not os.path.exists(backup_path):
+            os.rename(input_path, backup_path)
+            print(f"  Backup created: {filename}.backup")
+        else:
+            input_path = backup_path
+            print(f"  Using existing backup")
+
+        # Resample
+        output_path = os.path.join(sounds_dir, filename)
+        if resample_wav(input_path, output_path, target_rate):
+            print(f"  ✓ Successfully resampled to {target_rate}Hz")
+        else:
+            print(f"  ✗ Failed to resample, restoring backup")
+            if os.path.exists(backup_path):
+                os.rename(backup_path, output_path)
+
+    print("\n" + "=" * 50)
+    print("Resampling complete!")
+    print("\nBackup files (.backup) have been created.")
+    print("If everything works, you can delete them.")
+
+if __name__ == "__main__":
+    main()