[Feature Request]: Docling must be installed before starting server

[danielaskdd]

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Feature Request Description

The Docling package is quite large, takes a long time to install, and is prone to errors. Therefore, it is not recommended to dynamically install Docling when the LightRAG server starts.

Instead, if the server detects that the document extraction option has enabled Docling during startup, it should check whether Docling has been properly installed. If not, it should prompt the user to manually install Docling first and refuse to start the server.

Additional Context

No response

[danielaskdd]

Plang to use MinerU server instead of build-in file extractor. Docling should change to independent server also.