Add Roughtime as an additional time source

[Heime-Jorgen]

Summary

OpenTTT currently fuses timestamps from NIST, Apple, Cloudflare, and Google. Google Roughtime is a cryptographically signed time protocol specifically designed for tamper-evident time attestation — adding it would increase the trust surface and give PoT tokens a Roughtime-backed source.

Background

• Roughtime is an IETF draft protocol (RFC 9557 adjacent) that provides signed timestamps from independent servers
• It's already referenced in our ethereum-magicians discussion as a comparison to OpenTTT's pre-ingestion enforcement model
• Adding Roughtime as a source would let PoT tokens carry a roughtime entry in the sources array

Scope

• Implement RoughtimeSource class in src/sources/
• Query at least one public Roughtime server (e.g., Google's roughtime.sandbox.google.com)
• Parse the Roughtime response and extract signed timestamp
• Integrate with TimeSynthesis — add to the multi-source fusion array
• Add unit test with mocked Roughtime response

References

• Existing sources: src/sources/
• Roughtime protocol: https://roughtime.googlesource.com/roughtime
• IETF draft: https://www.rfc-editor.org/rfc/rfc9557

Difficulty

Low-Medium — TypeScript, no blockchain knowledge needed. Mainly HTTP/UDP parsing and fitting into the existing TimeSource interface.