Broken links to NIP-17 in spec.md

[BenGWeeks]

Summary

The spec.md file contains broken links to NIP-17. The links use relative paths that don't work in this repository.

Current (Broken)

[NIP-17](17.md)

This relative path format only works within the official nostr-protocol/nips repository.

Suggested Fix

Replace with absolute URLs:

[NIP-17](https://github.com/nostr-protocol/nips/blob/master/17.md)

Or use the nips.nostr.com format:

[NIP-17](https://nips.nostr.com/17)

Affected Locations

The broken link appears in multiple places:

• Required Components section
• Core Flows section
• Order Communication section

Thanks!