Docs have dead links

[mitroko]

Describe the bug
Hello, looks like links published on https://github.com/modelcontextprotocol/registry/tree/main/docs are dead and no longer valid, please fix and add test cases to cover link validity (at least parse 404 codes)

To Reproduce

1. visit https://github.com/modelcontextprotocol/registry/tree/main/docs, try to follow guide links

Expected behavior
Links are valid and forward to pages that exists

Logs
N/A

Additional context
N/A