docs: add arcana signer

[avasisht23]

Pull Request Checklist

• Did you add new tests and confirm existing tests pass? (yarn test)
• Did you update relevant docs? (docs are found in the site folder, and guidelines for updating/adding docs can be found in the contribution guide)
• Do your commits follow the Conventional Commits standard?
• Does your PR title also follow the Conventional Commits standard?
• If you have a breaking change, is it correctly reflected in your commit message? (e.g. feat!: breaking change)
• Did you run lint (yarn lint:check) and fix any issues? (yarn lint:write)
• Did you follow the contribution guidelines?

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PR-Codex overview

Detailed summary

• Added Arcana Auth to the navigation menu in the Vitepress config.
• Added arcana-auth.ts file with imports and initialization code for Arcana Auth integration.
• Added arcana-auth.md guide for integrating Arcana Auth as a signer with Account Kit.

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[avasisht23]

Current dependencies on/for this PR:

• main
  • PR docs: add arcana signer #318 👈

This stack of pull requests is managed by Graphite.

[avasisht23]

@rthomare @moldy530 this is a dupe of #291 but I merged that into dev back then, not main. this is merging to main.