feat(cli): include display names in channel members

[kiranmagic7]

Summary

buzz channels members serialized the channel membership tags directly, so each record contained only pubkey and role. This change loads member profiles with one batched kind:0 filter and adds a nullable display_name to each record while preserving membership order and roles. The profile projection uses the relay's existing name fallback; missing or malformed profiles produce null.

Related issue

Fixes #4437. No duplicate implementation was found; the closest prior CLI mention work is #3330, which does not change channels members output.

Testing

• cargo test -p buzz-cli channel_member -- --nocapture
• cargo test -p buzz-cli
• cargo clippy -p buzz-cli --all-targets --all-features -- -D warnings
• cargo fmt --all -- --check
• just ci

All checks passed. No screenshots are needed for this CLI JSON change.

[Chessing234]

looking at this for #4437 — if you're joining display names via users bulk on the same pubkeys from the membership event, that matches how the relay does mention routing. please keep display_name nullable when a profile is missing so tooling can tell "no name" from "not returned".

[kiranmagic7]

Thanks, that is the contract in this branch now. display_name is added as JSON null when no profile/name is available, so callers can distinguish a missing profile from a returned empty string. The regression channel_members_include_nullable_profile_display_names covers that nullable path and I will keep it unchanged.