Was reusing netbird-zero-trust-mesh-topology.svg (the doc's detailed
peer-topology diagram) in the README too - breaks this repo's own
established convention of the README getting its own dedicated asset
even when covering related material (see readme-trust-boundaries-
blast-radius.svg vs architecture-overview-trust-depth.svg). New diagram
is a simple perimeter-vs-zero-trust conceptual contrast, matching the
README section's generalized framing rather than NetBird's specific
implementation topology.
