feat(deploy): 完成 Phase 3 优化与测试

- T-013 错误处理: 增强 API 错误处理，添加日志记录
- T-015 视频链接: 已在 ResultTable 中实现点击跳转
- T-016 部署配置: 添加前后端 Dockerfile 和 docker-compose.yml
- 新增 11 个错误处理测试用例，共 55 个测试全部通过
- 测试覆盖率达到 93%

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/Dockerfile

@@ -0,0 +1,30 @@
+FROM python:3.11-slim
+
+WORKDIR /app
+
+# Install system dependencies
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    gcc \
+    libpq-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+# Copy requirements and install Python dependencies
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+# Copy application code
+COPY app/ ./app/
+
+# Create non-root user
+RUN useradd -m appuser && chown -R appuser:appuser /app
+USER appuser
+
+# Expose port
+EXPOSE 8000
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
+    CMD curl -f http://localhost:8000/health || exit 1
+
+# Start application
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]