docs: clarify filter pipeline and lua hook scope

[suxb201]

Summary

• explain where the filter stage runs and add flow context to the English and Chinese filter guides
• clarify that the Lua function hook operates after filtering and trim unrelated issue references in both languages
• update the configuration chapter to describe the layered filter rule engine and Lua hook relationship

Testing

• not run (documentation only)

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https://chatgpt.com/codex/tasks/task_e_68db829e0028832484a0f46434f4521a