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/Dockerfile

@@ -0,0 +1,35 @@
+# Use Python 3.10 as base image
+FROM python:3.10-slim
+
+# Set working directory
+WORKDIR /app
+
+# Install system dependencies
+# espeak-ng is required for Kokoro TTS (grapheme-to-phoneme conversion)
+RUN apt-get update && \
+    apt-get install -y --no-install-recommends \
+    espeak-ng \
+    && rm -rf /var/lib/apt/lists/*
+
+# Copy requirements file
+COPY requirements.txt .
+
+# Install Python dependencies
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy backend code
+COPY . .
+
+# Expose port 8000
+EXPOSE 8000
+
+# Set environment variables
+ENV PORT=8000
+ENV LOG_LEVEL=info
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=40s --retries=3 \
+    CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:8000/api/health')"
+
+# Start Uvicorn server
+CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]