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>

pyproject.toml

@@ -0,0 +1,24 @@
+[project]
+name = "wedding-phone"
+version = "1.0.0"
+description = "Vintage rotary phone audio system for weddings and events"
+readme = "README.md"
+requires-python = ">=3.7"
+dependencies = [
+    "flask>=2.3.0",
+    "numpy>=1.21.0",
+    "pyaudio>=0.2.13",
+    "RPi.GPIO>=0.7.1",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=7.0.0",
+]
+
+[build-system]
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+
+[tool.uv]
+dev-dependencies = []