BYOK contribution write-back (platform)

[suung]

Branch: feature/byok-contribution-publish
Background
BYOK keys already on main. Missing: publish analysis results to platform. Not Actwyser.
Goals

• Publish analysis.result.* after backend-enhanced analysis.
  Acceptance criteria
• publish_analysis_result publishes to analysis.result.{id}
• Hooked from flow orchestrator when USE_BACKEND + resource_id
• Provenance mode is byok_contribution when flag set
• Unit test mocks NATS subject/payload
• Folder placement reviewed (report_analyst_jobs/ for now)