hackathon: REST routes required for PCAP demo compose

[xnorkl]

Hackathon scope

REST surface required for the PCAP replay demo compose only.

Principles

• Fixture protocol is TBD — do not assume HL7/DICOM or other named protocols on the capture until chosen.
• Broad REST audit, PATCH alignment across all verbs, VIPER-only cleanup, and topology-driven expansion are not part of this slice — see chore: REST API prune and refine (stretch / post-hackathon) #148.

Acceptance criteria

• Identify routes required for hackathon only and keep them stable.
• Anything broader → chore: REST API prune and refine (stretch / post-hackathon) #148 or backlog; do not block PCAP demo on full API cleanup.

Deferred / stretch

Full prune-and-refine umbrella (topology sequencing, PATCH alignment, sub-issue references): #148