fix(cli): list DMs from canonical metadata

[RossHartmann]

Summary

• list DMs from the canonical kind:39000 channel metadata already emitted by DM creation
• retain exact #p participant scoping and defensively require both t=dm and the viewer's p tag
• cover canonical DM recognition and rejection of streams or other participants' DMs

Why

buzz dms list currently queries kind:41001, but the relay does not produce that kind. Canonical DM creation already publishes kind:39000 metadata with d, participant p, and t=dm tags, so using that metadata restores inventory without adding another relay event shape.

Validation

• cargo fmt -p buzz-cli -- --check
• cargo test -p buzz-cli commands::dms
• cargo clippy -p buzz-cli --all-targets -- -D warnings

[github-actions]

🔐 Codex Security Review

Status: review required for the current range.

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