feat: improve Docker deployment and Dify API configuration

- Use environment variables for Dify API key/URL
- Add host.docker.internal support in docker-compose
- Add DATABASE_URL env and prisma db push to Dockerfile
- Clean up test/requirement files and add deployment docs

Dockerfile

@@ -11,6 +11,8 @@ FROM base AS builder
 COPY --from=deps /app/node_modules ./node_modules
 COPY . .
 RUN npx prisma generate
+ENV DATABASE_URL="file:./dev.db"
+RUN npx prisma db push
 RUN npm run build
 
 # 阶段3: 生产运行环境