Add buzz users set-status for the NIP-38 profile status line

[kaganin]

Summary

The desktop client renders a persistent user status (NIP-38 kind:30315, d:general) as the status line on profiles, but the CLI had no way to set it — only ephemeral presence (set-presence, kind:20001). Integrations that want a scriptable, durable status line (for example a now-playing music bridge that shows the current TIDAL track on a profile) had no entry point.

Screenshots

This adds:

buzz users set-status --text "Working on the relay" --emoji "🔧"
buzz users set-status --text ""   # clears the status

• Signs and submits the replaceable kind:30315 event via the HTTP bridge (no WS needed — unlike presence, user status is a stored event).
• Uses the d:general coordinate the desktop client already reads for the profile status line, and the same emoji tag shape SetStatusDialog publishes.
• Empty/whitespace text publishes empty content, which the desktop treats as a cleared status.

Test plan

• cargo test -p buzz-cli --lib — 250 passed (includes updated command-inventory tests for the new subcommand).
• Manually verified end-to-end against a live community relay: published a status from the CLI and confirmed the desktop client renders it in the profile popover status line, live-updating via the kind:30315 subscription.