Integrate compute service with the activity timeline

[scotwells]

Parent Issue

Tracked by datum-cloud/enhancements#682 (Launch Workload Compute Service — "UFOs")

Summary

Compute resources have no integration with Datum's activity timeline system. Users and operators have no audit trail for key instance lifecycle events — who deployed a workload, when an instance started or stopped, and what caused a termination. This work integrates the compute service with the platform activity system so that key events appear in the project activity timeline.

Goals

• Emit activity events for key compute lifecycle moments: workload deployment created/updated/deleted, instance started, instance stopped, instance terminated (with reason), instance failed
• Ensure events are attributed to the correct actor (user or service account) and project
• Events should appear in the project activity timeline in the Cloud Portal
• Follow the activity event conventions established by other platform services (see enhancements#666)

Non-Goals

• Real-time log streaming (tracked under observability issue)
• Metrics or billing events

Related

• enhancements#666 — Activity timelines for platform services