The client previously reported "Broadcast traffic flowing" as soon as either
broadcast TX or RX was nonzero. During the MVP DHCP/ARP proof, one-way
broadcast is useful but weaker evidence than bidirectional broadcast.
Keep the existing healthy message for two-way broadcast, but report
outbound-only broadcast as a warning that the client is still waiting for a LAN
broadcast reply, and report inbound-only broadcast separately. This makes the
Windows client status lines more precise when DHCP is stuck.
Test Plan:
- cargo test -p lanparty-obs
- cargo fmt --check
- cargo test --workspace
- cargo clippy --workspace --all-targets -- -D warnings
- git diff --check
- git diff --cached --check
Refs: MVP Windows DHCP diagnostics