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>

README.md

@@ -97,6 +97,7 @@ Web interface available at: `http://<raspberry-pi-ip>:8080`
   - pyaudio>=0.2.13
   - RPi.GPIO>=0.7.1
   - waitress>=2.1.0 (production WSGI server)
+  - scipy>=1.7.0 (audio resampling utility)
 
 ## Installation
 
@@ -506,7 +507,7 @@ The `config.json` file contains all system settings:
     "chunk_size": 1024,                    // Audio buffer size
     "format": "paInt16",                   // Audio format (16-bit)
     "channels": 1,                         // Mono audio
-    "sample_rate": 44100,                  // 44.1kHz sample rate
+    "sample_rate": 48000,                  // 48kHz sample rate
     "max_record_seconds": 300              // Max recording time (5 minutes)
   },
   "paths": {
@@ -527,6 +528,8 @@ The `config.json` file contains all system settings:
   "system": {
     "active_greeting": "dialtone.wav",     // Default greeting
     "extra_button_sound": "button_sound.wav", // Default button sound
+    "beep_sound": "beep.wav",              // Recording start beep
+    "beep_enabled": true,                  // Enable beep before recording
     "greeting_delay_seconds": 0,           // Delay before greeting plays (0-10)
     "volume": 70                           // Default volume (0-100)
   }
@@ -597,6 +600,39 @@ Look for your HiFiBerry device and note its index number, then set it in `config
 4. Check IP address: `hostname -I`
 5. Try localhost: `http://127.0.0.1:8080`
 
+### Audio Sample Rate Mismatch
+
+If you see errors like `Expression 'paInvalidSampleRate' failed` or warnings about sample rate mismatches:
+
+1. **Check your config.json sample rate** (default is 48000Hz):
+   ```json
+   "audio": {
+     "sample_rate": 48000
+   }
+   ```
+
+2. **Resample your audio files** to match the configured rate:
+   ```bash
+   # Using the provided resampling script
+   python3 resample_audio.py
+
+   # Or manually with ffmpeg
+   ffmpeg -i input.wav -ar 48000 output.wav
+   ```
+
+3. **Delete default sounds** to regenerate at correct rate:
+   ```bash
+   rm rotary_phone_data/sounds/dialtone.wav
+   rm rotary_phone_data/sounds/beep.wav
+   # These will be regenerated at startup
+   ```
+
+The `resample_audio.py` utility will:
+- Automatically detect the target sample rate from `config.json`
+- Create `.backup` files before modifying originals
+- Resample all WAV files in the sounds directory
+- Preserve stereo/mono and bit depth
+
 ### Configuration Errors
 
 If the script won't start: