Add UV package management and volume control feature

Features:
- Add pyproject.toml for UV package management
- Volume control with real-time slider (0-100%)
- Backend volume adjustment with numpy audio scaling
- Volume setting persists in config.json
- Debounced API calls for smooth slider interaction
- Enhanced audio playback with volume multiplier
- Update README with UV installation instructions
- Add volume control documentation

API Changes:
- GET /api/volume - Get current volume setting
- POST /api/volume - Set volume level

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

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

README.md

@@ -9,6 +9,7 @@ A Raspberry Pi-based rotary phone system for weddings and events. Guests can pic
 - **Voice Recording**: Automatically records guest messages after the greeting
 - **Web Interface**: Beautiful, responsive web UI for managing the system
 - **Audio Playback**: Play recordings and greetings directly in the browser
+- **Volume Control**: Adjust playback volume with real-time slider (0-100%)
 - **Multiple Message Support**: Upload and manage multiple greeting messages
 - **Active Message Selector**: Choose which greeting plays when the phone is picked up
 - **HiFiBerry Support**: Optimized for HiFiBerry DAC+ADC Pro audio quality
@@ -43,7 +44,30 @@ git clone https://git.b4l.co.th/grabowski/wedding-phone.git
 cd wedding-phone
 ```
 
-### 2. Install Dependencies
+### 2. Install UV (Recommended)
+
+UV is a fast Python package installer and resolver. Install it:
+
+```bash
+curl -LsSf https://astral.sh/uv/install.sh | sh
+# Or on Raspberry Pi with pip:
+pip3 install uv
+```
+
+### 3. Install Dependencies
+
+#### Option A: Using UV (Recommended)
+
+```bash
+# Install system dependencies
+sudo apt-get update
+sudo apt-get install -y python3-pyaudio portaudio19-dev
+
+# Install Python dependencies with UV
+uv pip install -e .
+```
+
+#### Option B: Using pip
 
 ```bash
 sudo apt-get update
@@ -51,7 +75,7 @@ sudo apt-get install -y python3-pip python3-pyaudio portaudio19-dev
 pip3 install flask numpy RPi.GPIO
 ```
 
-### 3. Configure HiFiBerry
+### 4. Configure HiFiBerry
 
 Run the automatic configuration script:
 
@@ -62,7 +86,7 @@ chmod +x configure_hifiberry.sh
 
 Or follow the manual instructions in `AUDIO_FIX.md`.
 
-### 4. Test Your Audio
+### 5. Test Your Audio
 
 ```bash
 python3 test_complete.py
@@ -73,7 +97,7 @@ This will test:
 - Dial tone generation
 - Microphone recording
 
-### 5. Configure GPIO Pin
+### 6. Configure GPIO Pin
 
 Edit `rotary_phone_web.py` and set your hookswitch GPIO pin:
 
@@ -82,7 +106,7 @@ HOOK_PIN = 17  # Change to your GPIO pin number
 HOOK_PRESSED = GPIO.LOW  # Or GPIO.HIGH depending on your switch
 ```
 
-### 6. Run the System
+### 7. Run the System
 
 ```bash
 python3 rotary_phone_web.py
@@ -96,21 +120,27 @@ The web interface will be available at:
 
 ### Web Interface
 
-The web interface provides three main sections:
+The web interface provides four main sections:
 
 #### 1. Phone Status
 - Shows current phone state (on-hook/off-hook/recording)
 - Displays active recording filename
 - Auto-refreshes every 5 seconds
 
-#### 2. Greeting Messages
+#### 2. Volume Control
+- **Adjust Volume**: Drag slider to set playback volume (0-100%)
+- Real-time visual feedback with percentage display
+- Changes apply immediately to greeting playback
+- Volume setting persists across restarts
+
+#### 3. Greeting Messages
 - **Upload**: Click "Choose WAV File(s)" to upload one or multiple greeting messages
 - **Play**: Click "▶️ Play" to preview any greeting in your browser
 - **Set Active**: Click "⭐ Set Active" to select which greeting plays when the phone is picked up
 - **Delete**: Remove unwanted greetings (cannot delete the active one)
 - **Default Tone**: Generate a classic telephone dial tone
 
-#### 3. Recordings
+#### 4. Recordings
 - **Play**: Listen to recordings directly in the browser
 - **Download**: Save recordings to your computer
 - **Delete**: Remove unwanted recordings
@@ -131,6 +161,7 @@ wedding-phone/
 ├── rotary_phone_web.py       # Main application
 ├── test_complete.py           # Audio testing script
 ├── configure_hifiberry.sh     # HiFiBerry setup script
+├── pyproject.toml            # UV/pip package configuration
 ├── AUDIO_FIX.md              # Audio configuration guide
 ├── README.md                  # This file
 ├── .gitignore                # Git ignore rules
@@ -279,6 +310,8 @@ The system provides REST API endpoints:
 - `GET /api/status` - Phone status JSON
 - `GET /api/recordings` - List all recordings
 - `GET /api/greetings` - List all greeting messages
+- `GET /api/volume` - Get current volume setting
+- `POST /api/volume` - Set volume level (0-100)
 - `POST /upload_greeting` - Upload new greeting
 - `POST /set_active_greeting` - Set active greeting
 - `POST /delete_greeting/<filename>` - Delete greeting