feat: Add Docker configuration for backend

- Create Dockerfile with Python 3.10 base image
- Install system dependencies (espeak-ng) for Kokoro TTS
- Install Python dependencies from requirements.txt
- Copy backend code and expose port 8000
- Configure Uvicorn server startup
- Add docker-compose.yml for easy orchestration
- Include health checks and environment variables
- Add .dockerignore to optimize build context

Implements task 6 - Requirements 11.1-11.6

backend/docker-compose.yml

@@ -0,0 +1,24 @@
+version: '3.8'
+
+services:
+  backend:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: text-to-audiobook-backend
+    ports:
+      - "8000:8000"
+    environment:
+      - PORT=8000
+      - LOG_LEVEL=info
+    volumes:
+      # Mount code for development (optional - comment out for production)
+      - ./services:/app/services
+      - ./main.py:/app/main.py
+    restart: unless-stopped
+    healthcheck:
+      test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:8000/api/health')"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 40s