Mycelia submodule clone fails due to missing commit reference

[futureisAJASU]

Summary

Cloning Chronicle with the Mycelia submodule enabled fails because the submodule
points to a commit that no longer exists in the remote repository.

Since Mycelia is optional, this currently blocks the setup for users who do not
intend to use it.

---

Steps to Reproduce

git clone --recursive https://github.com/SimpleOpenSoftware/chronicle.git

or

git submodule update --init --recursive

Actual Result

fatal: remote error: upload-pack: not our ref <commit>
fatal: Fetched in submodule path 'extras/mycelia', but it did not contain <commit>.

The clone/setup process stops here.

Expected Result

• Users should be able to complete setup without Mycelia, since it is optional.
• A broken Mycelia submodule should not block Chronicle installation.

Environment

• OS : Ubuntu(WSL2 on windows)
• Git version : default ubuntu package
• Chronicle setup via quickstart.md & README.md

Notes / Suggestions

1. Update the Mycelia submodule commit reference to a valid commit
2. Mycelia opt-in (do not require --recursive by default)
3. Document an official workaround for skipping Mycelia during clone/setup
4. Handle submodule failure gracefully during setup

I’m happy to submit a documentation PR clarifying that Mycelia is optional and how to proceed without it.