fix: down does not remove networks or named volumes

[Jaro-c]

Problem

engine/lifecycle.rs down_with_options removes containers but never:

1. LIFE-001: Removes non-external networks declared in the compose file. Over time this exhausts the host's network namespace limit.
2. LIFE-002: Removes named volumes even when --volumes (remove_volumes=true) is passed. Named volumes accumulate indefinitely.

Fix

After all containers are removed in down_with_options:

1. Iterate file.networks, skip external, remove each non-external network by its resolved name (ignore 404).
2. When remove_volumes, iterate file.volumes, skip external, remove each non-external volume by its resolved name (ignore 404).