docs: add GitBook setup, fix broken links, and generate API reference

[angpt]

Description

Updates GitBook setup, with auto-generated API Reference. Fixes broken links.

PR Type

• Documentation
• Infrastructure

Relevant issues

Checklist

• I understand the code I am submitting.
• I have added unit tests that prove my fix/feature works.
• I have run this code locally and verified it fixes the issue.
• New and existing tests pass locally.
• Documentation was updated where necessary.
• I have read and followed the contribution guidelines.
• AI Usage:
  • No AI was used.
  • AI was used for drafting/refactoring.
  • This is fully AI-generated.

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[njbrake]

I didn't verify each link but overall looks correct 🚀 Thank you!