Slice: Add WARP TTD participant discovery consumer fixture

[flyingrobots]

Slice

Prove that a Continuum-capable tool can discover a target through protocol profiles rather than app-specific adapters.

Done when:

• WARP TTD or a fixture consumer reads continuum.participant.hello.v1 descriptor output;
• consumer reports supported profiles and exact evidence posture;
• redacted and credential-required fields are preserved;
• the fixture does not require the target to be a runtime.

Part of #59.