bug: add get_document

[planetf1]

A missing CLI command to get a single document was added in AI4quantum/maestro-knowledge#62

The cli has now moved, so the original code is now in https://github.com/planetf1/maestro-knowledge/tree/customheader_withcli/cli/src

cli/src/get_document.go
cli/src/get_document_test.go

Added support this for.

Now need to

• incorporate into existing structure
• identify any other omissions vs the mcp server