apply_capability_change is Docker-only teardown/apply code. Before this
change it was called regardless of backend, so approving a capability-block
proposal from a smolmachines agent would run Docker commands against a
slug that has no Docker container.
After this change approve() reads the bottle's metadata: if compose_project
is empty (the smolmachines indicator) it raises CapabilityApplyError with
a clear operator message before any teardown runs. Docker bottles (non-empty
compose_project) and unknown bottles (no metadata) fall through to the
existing Docker path unchanged.
Closes#136
didericis-claude