Cleanup/deduplication of the v0.9.1 spec

The v0.9.1 [spec]() is a very minor incremental update over v0.9, however it contains a lot of duplicated code and text, making it appear much more complex than what it needs to.

In some cases, the data in the spec is wrong, for example in the basic catalog example JSON responses, the version of the protocol is `v0.9` instead of `v0.9.1`.

Should we clean-up the v0.9.1 to make it just an "extension" of v0.9 (pointing back to v0.9 as needed?)

Look at the v0.9.1 spec file in the repository, likely in a docs or spec directory. Identify duplicated sections and compare with the v0.9 spec. Update the version references (e.g., protocol version in JSON examples) and restructure to reference v0.9 where possible. Verify changes by checking the spec's consistency and correctness.

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