Shared fixtures build DockerBottlePlan and SmolmachinesBottlePlan from
identical git_gate_plan and egress_plan inputs and assert that both
backends render the same git gate lines (name → host:port) and egress
lines (host [auth:scheme] when authenticated, host alone otherwise).
Move git_gate_plan, egress_plan, supervise_plan, and agent_provision
from DockerBottlePlan and SmolmachinesBottlePlan into BottlePlan.
Replace the abstract print method with a single concrete implementation
that renders git gate entries as "name → upstream_host:upstream_port"
and egress routes with conditional "[auth:scheme]" annotations.