Improve Redis connection handling

[ohld]

Summary

• add configuration for Redis health checks and enable socket keepalive on the async connection pool
• wrap the meme queue pipeline usage in an async context manager so connections are released properly

Testing

• pytest (fails: missing optional test dependencies such as pytest_asyncio, sqlalchemy, and orjson in the environment)

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https://chatgpt.com/codex/tasks/task_e_68dc050362b88326b3e20da30203a807