Added background, crop to round, with transparency using GIMP.

Kinda unrelated really.

Generated with Nano Banana. I forgot the exact prompt but it was something like
this:

"Generate an image of a nixie, inside the NixOS logo with half the body behind
the logo, chin rest on hand, slightly smiling, cartoon style with large stroke,
used for a logo fits in square composition"

Took a few retries.

Still need it for some environments where there's no DHCP, and might be
useful for IPv6 support in the future.

Simple implementation for now, unless we need complex state tracking
later, we don't need dedicated state manager.

Custom agent and API are just implementation details, not features.

For future shared mutable state.

Needs to wire this to the API.

Need a bit more freedom than the sandbox for now, may revisit later.

More like README driven development.